/\.
rrA-
The Mechanics
0/ Fitting Glasses
By
Robert D. Pettet
Giving complete information concerning
fitting, adjusting and prescribing eyeglass
and spectacle frames and mountings, and
covering all mechanical work within the
province of the refractionist.
PUBLISHED BY
TOPAZ & KAEMERLE
CHICAGO
OPTOMETRy
Copyright
1913
Introduction
THE purpose of thi^ book is to impart to the refrac-
tionist information regarding the mechanical side
of fitting glasses, principally the adjustment and
fitting of eyeglass and spectacle frames and mountings.
It is designed to meet the great demand for data of this
kind presented in a practical way and which are omitted
from text books on refraction. The descriptions and in-
structions are confined to modern types of eyeglasses and
spectacles, and antique styles are not discussed except
where they have some bearing on present day fitting.
The book has for its foundation the extended prac-
tical experience of the author and observation of the
methods of others that have come to his attention.
Table of Subjects
Definitions and illnstrations of different styles and parts
of eyeglasses, spectacles and lenses.
Inset and Outset studs explained.
Miscellaneous frames and mountings described,
Miscellaneous lenses described.
How to ascei'tain the correct frame or mounting.
Measuring the pupillary distance, only one correct way.
Measuring for and the fitting of spectacles.
Measuring for and the fitting of eyeglasses.
How to fit frames and mountings containing l)ifocal
lenses.
How to adjust spectacles.
How to adjust eyeglasses.
Kinds of pliers to use.
How to judge a good fingerpiece eyeglass mounting.
How to write prescriptions.
Drilling of holes in lenses.
Ascertaining the power of lenses.
How to ascertain the position of the plus and minus
cylinder in compound lenses l)y simple inspection.
How to construct a chart to measure prisms and to detect
a prism i^ower in lenses.
Transpositions simplified.
How to de-center lenses to obtain definite prism powers,
formulas, etc.
How to mount rimless lenses.
What to do for loose screws.
Record systems.
Definitions
Frames : Fixtures that have rims going around the
lenses.
Mountings : Fixtures that hold rimless lenses.
Speetaeles: Fixtures that are held in position by
means of bows (temples) that go around the side of the
head and by a bi-idge that rests on the crown of tlie nose.
When these have rims aromid the lenses they are known
as spectacle frames and when there are no rims around
the lenses they are known as spectacle mountings.
Eyeglasses: Fixtures that are held in position on
the nose by springs and l)y guards that press on the sides
of the nose. With rims around the lenses they are eye-
glass frames and without rims they are eyeglass
mountings.
Spectacles
Temples: Attachments on spectacles that go around
the side of the face and over the ears. Straight temples
go straight back and do not circle the ears. Riding
temples (sometimes called riding bows) go entirely
around the back of the ears. Half-riding temples are half
way between the straight temple and riding temple vari-
eties, just turning slightly over the back of the ears.
Regular Temples : The ordinary wire temples.
Cable Temples: Made by wrapping two pieces of
pliable wire about each other.
Half-Cable Temples: The part from the frame to
the top of the ear is of the regular stiff wire, the part
9
10
THE MECHANICS OF FITTING GLASSES
Spectacle Mounting.
going aruuiul the cars is cable. There are several vari-
eties of this kind: C'onifort Temples, Apex Temples,
Velvet End Temples, etc.; these are very similar in con-
strnetion and ditfer only in the manner in which the soft
j)ortion that encircles the ear is attached to the wire that
goes to the frame. They are all very soft and pliable on
the ear end and are intended to increase the amount of
Spectacle Frame.
comfort and eliminate the features of the regular wire
temples that tend to make the latter uncomfortable about
the ear.
Bridge: The part of a spectacle that rests on the
nose and connects the two lenses. This is the central and
most important portion of a spectacle.
Shanks : The ends of the bridge that point outward
from the nose and connect with the lenses.
Straps: The attachments at the end of the shanks
and tem})]es on rimless ^nounliiigs by means of which the
lenses are held to the mounting.
THE MECHANICS OF FITTING Cxi.ASSES
11
End-pieces: The parts to which the temples are at-
tached in rimless mountings; they include the straps
which are really a part of them. When spoken of in con-
nection with temples they are familiarly known as
"ends," for instance, we speak of "temples and ends."
Eye-wires: The rims that encircle the lenses on
frames.
Eyeglasses (Regular) ,
Eyeglass Mounting.
Eyeglass Frame.
Spring: The central part of the frame or mounting
corresponding to the In-idge of spectacles. There are sev-
eral styles of springs as shown l)y the illustrations given
here. In addition to the dit¥erent varieties there are dif-
ferent sizes; the usual length of the oblong style is 21/8
inches, and of the hoop style 2 inches. Oblong springs are
sometimes called "square" springs and hoop springs are
sometimes called "oval."
u
F"ull. Reduced.
GRECIAN
Tilting.
Adjustable,
12
THE MECHANICS OF FITTIXC; Gf. ASSES
Guards: Tlie parts that lie against the side of the
nose and hold to the flesh; often called by the laity
"elips." By consult ing catalogs of the wholesale optical
houses it will be seen that there are countless styles and
designs. A few of the most common are shown here.
^
Wells.
Anchor.
Schwab. Anatomical. Bausch. Solid.
Studs: The parts that hold the lenses to the mount-
ing and which join the guards and the spring.
Open Studs: Those in which the nasal side of the
studs is left open.
Box Studs : In these the portion into which the
guard and spring fit is constructed like a ])ox and the
nasal side is closed, the stud-screw is countersunk, and
thus tliere are no rough parts or exposed screws in con-
tact with the flesh.
In addition to these two styles there are many sizes,
that is, some have longer posts than others, the purpose
of which is to regulate the distance between the lenses.
There are also ''drop" studs to lower the lenses; these
are made in two sizes — 1-1(5 i\\n\ 1-8 inch.
ABODE
From tlic illiisti-ation it will be observed that the
sizes of studs (controlled by the length of the post) are
THE MECHANICS OF FITTIXG GLASSES 13
indicated by the letters A, B, L\ D, E, and F ; A l)eing the
shortest and F the longest, with about one niillinieter be-
tween each succeeding size.
Inset and Outset Studs: Confusion exists in tlie
mind of every beginner in the matter of inset and outset
studs, and it must be admitted that there is good reason
for this, and the beginner cannot l)e criticized for any
misunderstandings he may have in this regard, for the
fact is there is so much difference of opinion in the minds
of various opticians and wholesale houses that it is never
safe to specify "inset" or "outset" until you know what
the person or house to whom you are writing means by
these terms. Most whok^sale catalogs state that inset
studs set the lenses farther from the eyes and that outset
studs set the lenses closer to the eyes. To the mind of the
average man who has not become accustomed to this
translation of the terms they will seem to be reversed.
Where this usage of the terms originated was with the
idea that inset studs set the mounting in toward the face
and consequently the lenses were set farther from the
eyes, however when we realize that the mounting always
stays in the same position on the nose and it is the lenses
themselves that are moved it would most certainly seem
that studs that set the lenses out should be termed "out-
set," but the term is not generally accepted this way, so
that the safest plan in writing prescriptions, etc., that you
are sending away to be filled is always to say "to set the
lenses closer to the eyes" or "farther away," as may be
wanted, for instance: "Inset studs, to set the lenses
farther from the eyes" or whatever way you want to put
it, so that what you want will be clearly understood.
14 THE MECHANICS OF FITTING GLASSES
Eyeglasses (Finger-Piece).
Bridge: Same as the bridge in spectacles. This
usually includes the studs, as they are generally made in
one piece.
Finger-pieces : The projecting ends in front that are
grasped by the tips of the fingers in order to operate the
spreading of the guards.
Springs: These connect directly with the guards
and cause them to press inward toward the nose.
Finger-i^iece eyeglasses are made in a great number
of styles and combinations and are given particular names
by the various manufacturers. While eyeglasses of this
design appear at first sight to be very much alike, closer
inspection and study will show that there are several
classifications. This subject is discussed in another por-
tion of this book under the heading ''How to Judge a
Good Finger-piece Eyeglass ]\rounting. "
Miscellaneous Frames and Mountings.
Grab fronts are fixtures to contain lenses, usually the
addition for reading, whicli attach to the outside of spec-
tacles, and may be taken off and ]uit on without removing
the spectacles proi)er. Grab fronts may be either with
THE MECHANICS (3F FITTING GI.ASSES
15
rims or rimless. Grab l)acks arc similar to grab fronts
except that they attach to the back of the spectacles in-
stead of the front.
Specalettes are a combination of eyeglasses and
spectacles, that is they are eyeglasses with temples. These
are desirable where the patient has a straight and nearly
vertical nose and experiences difficnlty in retaining a
spectacle bridge in the proper position and in cases where
the skin on the front of the nose is very sensitive. There
are several forms of these monntings and catalogs of
wholesale optical houses should be consulted on the
matter.
General Description of Dif-
ferent Kinds of Lenses.
It is thought that the simple forms, like double con-
cave and convex and periscopic concave and convex, are
so well known and understood they need no explanation,
so we shall proceed at once to the more advanced types.
Toric : A lens having three curves. It has the ap-
pearance of a very deep periscopic, having one side deep
convex and the other deep concave. By reason of its defi-
nition a toric lens can never be a sphere, but is always
either a cylinder or sphero-cylinder. Tories are built on
three base curves — the 3, 6 and 9 D.
Meniscus : A lens built on the deep periscopic form.
This kind of lens is always a sphere and is often, though
incorrectly, called a "spherical toric." This latter term
has come into such common use that it is generally ac-
cepted without question, in fact there are many in the
business who do not know that the term is technically
wrong.
Bifocals: Any lenses that are composed of two
parts or have two foci. Usually these lenses combine
the distant and near correction, the upper part for dis-
tance and the lower for reading.
16
THE MECHAXirS OF FITTING GLASSES
17
Cement Bifocals: Any Infoeal lenses in which the
reading or near correction segments are attached to the
main lens by cement, bnt nsnally understood to mean
bifocals where the segments (or scales) are not especially
thin and which are elliptical in shape.
Opifex Bifocals: Lenses in which the reading seg-
ments are very thin, usually round, and attached to the
main lens by cement. Sometimes called "semi-invisible"
bifocals.
Kryptok Bifocals: Lenses in which the reading seg-
ments are practically invisible and in which the segment
is fused to the main lens forming one piece of glass. The
segment and main lens are of different indices of refrac-
tion. There are other makes of fused bifocals, but the
Kryptok is the most widely known and used.
Perfection Bifocals: Lenses composed of two sep-
arate pieces of glass held in position by the rims of the
frames.
18
THE MPX'HANICS OF FITTING GLASSES
LentioTilars: Lenses of n iiiiims power in which the
peripheral i^ortions have been gronnd off flat or to a
convex edge for the pnrpose of lightening the weight of
the lenses and m.-ddng them thinner on tlie edges.
Ova! 1.1 nil
Round Lenticular
Colored Lenses: There are many different kinds
and colors used, the prime pnrpose being to reduce the
amount of light that enters the eye. Smoked lenses are
made in varying shades and densities. There are also
green and blue lenses. Much has been claimed recently
for amber lenses with the idea that they reduce the num-
ber of ultra violet rays entering the eye. Likewise claims
have been made for pink and amethyst shades. There
are also lenses known by special trade names most of
which are a combination of light green and light amber.
TABLE OF SIZES OF LENSES,
Eye
Inserts.
Rimless.
Short Oval
E.ve.
Inserts.
mm
mm
Rimless.
mm
Jumbo
4fi x38
46 x3S
44.. 5x39. r.
2
35x25.5
(1000
■H.3x3(!
44 x36
42.5x37.5
3
34x25
000
40.9x.31. 9
41 x32
39.5x33.5
4
33x24
00
39.7x30.7
40 x31
38.3x32.5
A
39x25
37.Sx28.S
3S.5x29.5
37 x31
B
40x26
1
30.5x27.5
37 x28
35.5x29.5
C
37x21
Shapes of Lenses.
In the iiiajoi'ity of cases regular shape lenses should
be used, but the short oval is very advantageous many
times. Where the patient does a great amount of near
work the short oval offers a large field of vision up and
down, the direction in wliich it most needed. This shape
is also desirable in cases of narrow P. I)., for here it is
usually necessary to use small lenses which naturally
restrict the field of vision.
The leaf shape is designed for peo])le having heavy
protruding brows ; it resembles the short oval with the
top rounded off. Odd shapes of lenses — that is, any but
the regular and short oval — should be generally avoided,
for their appearance is far from pleasing and gives a
suggestion of grotes(iueness to the face.
Regular Oval.
Short Oval.
Leaf Shape.
19
Ascertaining the Correct
Frame or Mounting.
The Unit of Measure.
The English system of lineal measnres has so long
been nsed in our everyday life that it is natural that this
system has lieen employed by American opticians in giv-
ing dimensions of spectacles, etc., but since we have
arrived at a place where accuracy and definiteness are
essential, this system is no longer practical. The con-
tinual use of fractions permits the occurrence of too
many errors and a specification of 1-8 or 1-16 inch gives
room for too much variation one way or the other,
whereas, if we measure by the metric system when dealing
with short distances we eliminate a large portion of the
element of error both in calculations and in the matter
of personal equation.
For instance, suppose we have 2V8 and 2yo inches to
comjjare. We have a general idea regarding the relation
of these two quantities and after a little thought we
realize there is a difference of % inch. Now express the
same dimensions in millimeters — we have 53 and 62 milli-
meters. At a glance we have a definite appreciation of
the relation and know instantly that there is a difference
of 9 millimeters. Then again, on a scale graduated in
millimeters the divisions are comparatively close together
and a slight variance around the mark becomes evident
20
THE MECHANICS i)V FITTIXC GLASSES 21
at once. I'pon a iiioint'ut \s reHectioii ;iii(l especially at"ter
we get deeper into this snbject, you will i-cadily appreci-
ate the advisability of nicasni'inii- in inillinictcrs instead
of inches.
Pupillary Distance.
There is just one simple method of ascertaining the
exact distance between the eyes.
Place yourself in a position directly facing the pa-
tient. Suppose you desire his P. D. for distance: Have
the patient look over your head at an object on the wall
opposite. Hold the rule in your right hand in the same
manner as you would a pencil and steady your hand
by placing your free fingers upon the side of the patient's
head. Now, with your left eye (right eye closed) bring
the zero of the rule opposite the line of demarcation be-
tween the iris and sclera, say, for instance in this case,
on the nasal side of the eye. Holding the rule in this posi-
tion quickly open your right eye and close your left and
read off the graduation mark opposite the edge of iris (in
this case temporal side) of patient's left eye. This read-
ing will give the true width between the eyes. Of course
if you measure from the nasal side of one eye you meas-
ure to the temporal side of the other eye and vice versa.
If you measure with both your eyes open your result
will vary 2 or 3 millimeters, because you will not be sure
which mark is opposite patient's eye. If you measure en-
tirely with one eye the error of parallax will enter so
much that your readings will always l)e from 2 to 5 milli-
meters too narrow.
To prove the veracity of the foregoing statements,
make two marks about two inches apart on a piece of
22
THE MECHANICS OF FlTTIXCx Cxi, ASSES
j)a}»('r; lay the ]);ii)('r on your desk and rc'sting yonr hand
on it liold your rule one or two inches above it. First
measure the distance with both eyes, then measure it en-
tirely with one eye, and then with each eye separately
(the zero with the left and the total width with the right
eye) and you will find a decided variance in your three
readings. By laying the rule Hat on the paper and meas-
uring the exact distance you will find your third measure-
ment to be correct.
This cut shows the method of measuring the i)u-
pillary distance, the P. D. in this case being 55 milli-
meters, measured from the inside of the right iris to the
outside of the left.
P.Z7.
THE MECHANICS OF FITTING GLASSES
23
The Spectacle Bridge.
There are two ways of expressing the dimensions of
a bridge: By giving each dimension in figures or by
using the size letter and number.
T h e dimensions considered are
height, inclination of crest, angle
and width of base. The following
letters are used to designate the
width of bridges, beginning with the
smallest: L, M, N, 0, P. The heights
are expressed in combination with
the letters by numbers, as i/o, 1, IVo,
2, etc. The shanks are called regular,
long and extra long. With the regu-
lar shanks the lenses are held a trifle
closer to the eyes than the crest of
the bridge; with long shanks the
lenses and crest of bridge are on the
same plane; with extra long shanks
the lenses are further from the eyes
than the crest of bridge is. Thus to
set the lenses away from the eyes to
escape the lashes, etc., we use long
and extra long shanks. When no
length shank is stated "regular" is
understood. This is the way the
different sizes of bridges are ex-
pressed: M, Mi/o, N2 extra long
shanks.
When the sizes' are not specified
as above it is necessary to give all the
dimensions in figures. The height of
DIMENSIONS OF SAD-
DLE BRIDGES.
Upper figure Incnes,
lower figure Millimeters).
Bridge.
Height.
w
a
n
L
5 8
IS
I.>2
V-'i
15
LI
H
3
IS
M
1.4
^8
IS
5-8
15
Ml
3^
Mil 2
1,4
15
M2
\-4
6
fc
17
18
H
18
N
14
N>4
!^,.
t,
Nl
1,;
3
4'-;
14
NIH
1'^
N2
■i
,•'4
18
20
•Hi
2C
N2y2
tv.
3
N3
^
IH
>8
21
21
Ol
3
IH
02
6
14
J8
21
03
9
ti
.a
23
PI
i-8
3
14
1
25
P2
'i'
ik
1
25
1
26
P3
■-
H
3
1
24 THE MECHANICS OF FITTING GLASSES
bridge is the distance above or below a line running
through the center of the lenses to the lower edge of the
center of bridge; the inclination of the crest is the dis-
tance from the inside plane of the lenses to the upper
edge of the middle of the bridge and is specified "in" or
"out," meaning in back or in front of the lenses, respect-
ively. The angle of the bridge is considered with respect
to the plane of the lenses, the latter being 90 degrees.
The angle is measured at the center or crest of the bridge.
Temples.
The length of temples is measured from tip to tip,
that is, from the screw hole to the extreme other end.
The average length is six inches, but they are also made
in lengths of 51/2, 6V2 and 7 inches.
Sizes of Lenses.
"Size eye," as it is familiarly called, represents the
outside measurement. The regular sizes are jumbo, 0000,
000, 00, 0, 1, 2 and 3, beginning at the largest and going to
the smallest. The "size eye" of frames agrees with the
size of the lenses.
"Pupillary Distance" is a term so often used in the
business that we have come to know it familiarly by its
abbreviation, P. 1)., so that in this book we shall always
refer to this dimension as P. D. instead of writing the
words out in full.
THE MECHANICS OF FITTINC CLASSES
25
The cut Oil this page illustrates a ineasuring eard
used for measuring spectacle frames. Your wholesale
house will supply you with one of these cards.
•25-*.
50 60 ^0 TM
PUPILLARr DISTANCE
To measure P. D. and height of bridge, place end
pieces on line A-A with inner edge of left eye at line B.
The figure at right end of right lens indicates the pupil-
lary distance and that at under edge of bridge crest indi-
cates the height of bridge.
To measure bridge crest, forward or back, place
lenses in slots, top down, with inner surface of lenses on
lower edge of slots. That edge of bridge resting on card
will indicate position of crest.
It will be noticed that in measuring the "pupillary
width" of spectacles and eyeglasses, a similar plan is fol-
lowed as when measuring over the eyes; that is, the dis-
tance is taken from the nasal edge of one lens or rim
to the temporal edge of the other lens or rim. This is
most conveniently accomplished by using the ineasuring
card designed for this purpose shown here.
26 THE MECHANICS OF KITTING GLASSES
Measuring for Spectacles.
Be sure, Ijofore going- further, that you know exactly
all the details already given, otherwise you will get most
unsatisfactory results. For instance, you may take the
base of bridge to be from center of the turns of the shanks
and the optician who fills your order will take it from the
last points where the flesh touches the bridge, with the
consequence that the spectacles you receive will always
be from two to thri-e millimeters too narrow. The same
applies to all tli'.' other dimensions, hut this is cited as
being the most common error.
Provide yourself with a (i or (i'o-incli rule gradu-
ated in l)otli inches and millimeters; a measuring card,
and a fitting set of spectacle frames.
Seat yourself directly in front of the patient — do not
stand, it is awkwai-d and conducive to error. Measure
Spectacle Fitting Set.
THK MhlCHANK^S OF FITTING GLASSES 27
the ])ationt's I'. I), and note it down. Select Troni tlie
fitting set the hridu'e tli:it comes iieai'est to fittiiiii; the
patient's nose. Notice the use of tlie word ''nearest" in
the i)revious sentence — it is only once in a hundred times
at least that you will find a stock size that will exactly fit.
Height of Bridge.
Now for the i)roi»er hridge dimensions: AVith the
frame, just selected, on the patient's face, note whether
the lenses set too low or too high, hearing in mind the use
that tlie patient is going to make of his new glasses,
whether for reading, distance or hoth. The average line
of vision should he through the center of the lenses. Sup-
pose, in the case hefore you, the lenses in the fitting frame
set too low, say one millimeter. Now, if w^e move the
hridge down the lenses will go up a corresponding
amount, so in this case, the hridge we want should he one
millimeter lower than the one on the fitting frame. Take
the frame from the patient's face and measure the height
of this hridge; suppose you find it to be four millimeters.
We found this was one millimeter too high, so the bridge
we want should be three millimeters in height. Mark it
down on your prescription pad.
Position of the Crest.
Replace the frame on the patient's face. Note
whether the lenses set too close or too near the eyes.
Suppose you find the lenses touch the lashes and need to
be set two millimeters farther out for ihe lashes to clear.
Take the frame off and measure the position of the
crest of this l»ridge, using the measuring card for this
purpose. Suppose you find it to be three millimeters out,
then as w^ith this bridge the lenses are two millimeters too
28 THE .MECHANICS OF FITTIXG GLASSES
close to the eyes, the bridge we want shoukl be two milli-
meters farther back than it is, whieh gives us one milli-
meter out (or forward) that the bridge crest should be.
Note this down under Position (or inclination) of Crest.
Width of Base.
Place the fitting frame on the patient's face, using a
bridge of sufficient width to allow the crest to strike the
nose; push the frame to the right or left so that all the
space between the l)ridge and nose will be on one side.
By ascertaining how much this space is you know how
much too wide the bridge is, and by measuring the bridge
and making the deduction for oversize, you have the
projDer width.
Pemember, that the base width is measured from the
point on each side where the flesh last touches and not
from the middle of the turns of the shanks. The width
of ])ase is one of the most important dimensions of the
bridge and decides to a large degree whether the spec-
tacles are comfortable or not. The ])ridge should tit the
nose just like a saddle, for if it touches all around it will
help support the weight and relieve some of the strain at
the back of the ears. At the same time a bridge too nar-
row at the base will press into the nose and be very
uncomfortable.
Angle of the Crest.
The average angle subtended by the bridge of the
nose is 45 degrees, the plane of the face being DO; in other
words, the more vertical the nose the higher will be the
nuniljer wliich represents its angle. To measure this
angle liold a i-ulc oi- card pci-pcMidicnlar to the plane of
tlie face and note the size of the angle between the rule
and the nose where the spectacle bridge will rest.
THE MECHANICS OF FITTING GLASSES
29
There are cards made to take this measurement, as
well as other littk' coiitrivaiices. Here are shown two
popular crest measures.
Length of Temples,
There are two ways of expressing the length of tem-
ples desired, i. e., the distance to hack of the ear or the
entire length of the temple from tip to tip. The first
measurement is made with the fitting spectacles on the
patient's face, the two extreme points l)eing the plane of
the lenses and the middle of the hack of the ear. The
other method is to notice how the length of the temples
on the fitting frame suits, measuring the full length of
these temples and then adding to or suljtracting from this
length as may be necessary.
The instructions given here api)iy to both rimless
and frames. Some use four or five spectacles of different
sizes to measure over, hut the use of a complete set of
12 sizes is strongly advised.
30
THE MEC^HANICS OK FITTING GLASSES
Eyegl
asses.
Finger-Piece. Regular.
The finger-) )i('('(' ty])e has eoiiie into use within tiie
hist ten years and on acconnt of neatness of api)earance,
the property of i-etaining its original shai)e and adjnst-
ment, and simplicity in fitting, it has become very popuLar
and widely used. However, there are cases where the
regular style is more desirable than the finger-piece and
vice versa. For instance, a finger-piece mounting has a
tendency to cause the nose to appear shorter and the face
narrower, while the regular mounting gives rise to re-
verse impressions. This l)eing the case if you put a
finger-piece mounting on a short nose you make it seem
shorter; a regular mounting would lengthen it. If you
fit a finger-piece mounting where the pupillary distance
is comparatively narrow, the eyes will seem still closer
together, whereas a regular mounting will seem to put
more space between the eyes.
"Regular" Style.
To ascertain the correct size of lens, length of stud,
style of gnai'd, etc., it will be (piite necessary to have an
eyeglass mounting to measure over.
First measure the j)atient's P. I). 'IMicn adjust your
sample mounting as well as you can and place it in the
THE MECHANICS OF P^ITTINCJ GLASSES 31
correct position on the patient's nose. Now measure the
P. D. of tlie .glasses while on the face (measure from in-
side edge of one lens to outside of the other) ; this places
you in position to know liow large to make the lenses and
how long the studs. Suppose, for illustration, that the
sample mounting is equipped with regular B studs and
eye lenses, that your patient's P. D. is 60, and that the
P. D. of the glasses, when on, is 58 millimeters. You see
at a glance that these glasses would be too narrow and
their P. D. must be increased 2 millimeters.
There are two ways in which this can be accom-
plished ; by using longer studs or larger lenses. The next
size studs to those on the sample mounting are known
as C studs, there being a ditfereuce of one millimeter in
the length of a B and a C. By using C studs in the case
we are considering we will increase the P. D. of the
glasses 2 mm. (Imm. on each stud), and thus obtain the
desired width of GO mm. By increasing the size of lenses
2 mm. and leaving the studs as they are in the sample
(B size) we can ol)tain the same result. The lenses in our
sample are eye size and their length therefore is
39 mm. ; adding 2 mm. to this gives 41, which is the length
of 000 eye lenses, hence by using 000 lenses and B studs
we obtain the desired P. D. With these two methods we
can make several combinations and get exactly the dimen-
sions we want. For instance, we have studs ranging
from A to F (about 1 mm. difference for each size) and
lenses ranging from 1 eye to jumbo, or in figures, from
37 to 46 mm. long, which we can combine in a great many
different ways.
Notice when the mounting is in the proper position
on the nose whether the lenses are too close to or too far
32 THE MECHANICS OF FITTINC 01. ASSES
away from the eyes. If they arc too close use inset studs
to put them farther out, if too far away use outset studs
to bring them closer. Both of these styles are made in
two sizes, 1-16 and 1-8 inch, and you can easily tell which
size is required.
If the l)rows are prominent and press against the
spring use a Grecian or a tilting spring. Oblong springs
are usually used for men and hoop springs for women,
but this is a matter of personal choice.
The guards selected should have a Hat surface where
they come into contact with the flesh — this is the first
requisite of an efficient guard. In adjusting the guards it
must be borne in mind that contact and adhesion count
greater for desirable results than pressure, and for this
reason the guard must be curved and bent to conform
with the corresponding part of the nose.
You should have about six eyeglass mountings, com-
plete with lenses, and having different styles of guards
and springs. With this equij^ment you can select the
style of guard that will be best for each particular case.
Some styles and angles of guards will set the lenses
lower than others, but usually it is necessary to drill the
holes in the lenses 1-16 or 1-S inch above center to lower
them, especially wIkm'c the glasses are to be bifocal or
reading lenses, in regular eyeglass mountings.
Finger-Piece Eyeglasses.
You must be provided with a complete fitting set of
some good make of mountings. Do not make the com-
mon mistake of getting a few mountings of several kinds,
but get a full set of some one particular style; if they are
good mountings, with the pi'oixT adjnstmciit, they can
THE MKCllAXli'S OF FITTING GLASSES 33
be inado to tit any nose llial could wear eyoo-lasses, and
by gettini;' a full sot yon liavo the ontifo rang'o of num-
bers and sizes to select from.
With the fitting- set at hand, select the mounting that
comes nearest to fitting, take your pliers and adjust the
mounting so that it will assume just about the same posi-
tion that the mounting you order will when adjusted.
Some manufacturers do not advise adjusting the mount-
ings in tlie fitting set, but experience proves that it is bet-
ter to do this, for you are then in position to know defi-
nitely whether the mounting can be made to fit or not,
and to accurately ascertain the size of lenses and the kind
of posts required.
Having decided what mounting fits the best, note the
number it bears that represents its size. Measure the
P. D. of the patient and then measure the P. D. of the
glasses. If these two measurements are alike prescribe
the same size lenses as those in the fitting mounting,
which is usually O eye size. If the fitting glasses are too
narrow in P. D. increase the size of the lenses until the
proper P. D. is obtained, provided of course that it is not
more than a few millimeters and does not make the lenses
too large. The 00 eye lenses are one millimeter longer
than eye size and will increase the P. D. just one milli-
meter; 000 eye lenses are two millimeters longer than
eye and will increase the P. D. the same amount. You do
not have to be controlled, however, by the standard sizes;
000 eye lenses have a length of -11 mm., you can use 42, 43,
or 44 mm. lenses if you desire. There is usually about
9 mm. diiference between the length and breadth of regu-
larly shaped lenses, so you can specify 42 x 33 or 43 x 34,
34 THE MECHANICS OF FITTING GLASSES
etc., instead of trying to convert these lenses to a
standard size. Likewise where it is desired to give a short
oval effect you may specify 42 x 34 or 42 x 35, etc., but
always remember that when you measure the P. D. of a
pair of glasses you measure from the inside edge of one
lens to the outside edge of the other lens and in this way
the length of only one lens is included in the total P. D.
and consequently au increase in the length of both lenses
of 2 mm. will increase the P. D. of the glasses only 2 mm.
and not 4 mm. as might at first be supposed.
Let us say that, in order to cause the glasses to have
the proper P. D. it would be necessary to use larger lenses
than are desired. In this case you must use extended
posts ; these correspond to the G and D studs in regular
eyeglass mountings and are made in just two sizes, 1-16
and 1-8 inch. Should you put on 1-16 extended posts you
will increase the P. D. Vs-i^^^li or about 3 mm. and % inch
extended posts would increase the P. D. i/4 i^ch or about
6 nun. Here it will be seen that both posts must be con-
sidered in the P. 1). as we include them both in the P. D.
measurement.
Now observe whether tlie lenses are too close or too
far from the eyes, if so prescribe inset or outset posts,
whichever are needed, the same as when fitting regular
mountings. Outset and inset |)osts are made in two
sizes, 1-16 and 1-8 inch, and it will l)e found compara-
tively easy to judge which size is needed.
Summing up, the things we need to know in prescrib-
ing finger-piece eyeglass mountings are: The number or
size of the mounting, extended, inset or outset posts and
the size of the lenses.
THE MECHANICS OF FITTING GLASSES 35
Fitting Mountings and Frames to Contain
Bifocal Lenses.
This is one of the most difficult branches of spectacle
and eyeglass fitting, and at the same time one of the most
important.
The greatest difficulty encountered by the wearer of
bifocals is getting them adjusted high enough to be able
to read without turning the eyes way down to escape the
upper edge of the segment and yet low enough to be able
to walk and to see distant objects. Right here is where
good judgment and ability to properly fit frames come
into play.
The vertical dimension of the bifocal segment should,
under average conditions, be just a trifle less than half
the height of the entire lens. The frame or mounting
should be made so that, when the patient 's head is upright
and his line of vision is straight ahead, the upper edge
of the bifocal segment is on a line with the lower edge
of the patient's iris. This, of course, will be subject to
variation, according to the distance the lenses set from
the eyes. If it is necessary to set the lenses well away
from the eyes, the lenses should be set lower and if they
are to be worn close to the eyes they must be set higher.
To tell just at what height the lenses should be placed,
put a pair of frames containing bifocals on the patient's
face and have him look straight ahead, then hold your
hand down in front of him at about the place he would
read and instruct him to look at it; note whether his line
of vision in each instance goes through the proper part
of the lens. By moving the lenses up or down you will
36 THE MECHANICS OF FITTING GLASSES
quickly see whether the frame you have on his face re-
quires raising or lowering and from this you can judge
how you want tlie holes drilled or what angle of guard
how high you want the bridge, or in the case of eyeglasses
you need.
In cases where the patient does a great amount of
near work, it may be found advantageous to use larger
bifocal segments, but of course, the larger the segment,
the more restricted will the distant field be.
There are many shapes of segments, the most com-
mon being the elliptical and the half-round. Nearly all
cement bifocals are of the former shape, while Kryptoks
(invisible bifocals) are usually about two-thirds of a
circle. While we are discussing Kryptoks it may be well
to state that this form of bifocal is not restricted to one
size and shape of segment. The regular size Kryptok
segment is about 14 mm. high and 18 mm. across ; larger
sizes can be had as well as the elliptical, similar in shape
to the regular cement bifocal.
In your practice you have come across many people
who have told you they could not wear bifocals and you
have also probably found that you have been able to sat-
isfactorily fit them with this kind of lens by exercising
care in the adjustment of the frame or mounting, and we
venture to say that the majority of people who say they
cannot wear bifocals would find the cause in the faulty
adjustment of the mounting rather than in the construc-
tion of the lenses. iWith this in mind we would urge those
who have experienced difficulty in fitting bifocals to make
a })jirti('ular study of frame fitting in connection with
bifocals.
How to Adjust Spectacles.
Before considering the adjusting of spectacles let us
analyze the conditions that must be presented by a prop-
erly fitting spectacle frame or mounting. The lenses
must center before the eyes and sit just as close as pos-
sible to the eyes without touching the lashes. In glasses
that are to be used for general work, i. e., both distant
and near, the line of vision should be just a trifle above
the center of the lenses when the eyes are directed
straight ahead. Every part of the frame must give entire
comfort; the bridge must fit all around the curve of the
nose like a saddle on a horse's back, and the temples
must be just the right length. Bear all the foregoing in
mind when fitting spectacles and the results will in-
variably be decidedly better than when some of these
points are ignored.
There are pliers that are specially designed to do
particular kinds of work, and it will be advantageous to
be supplied with the proper tools and to know their re-
spective uses, for you cannot accomplish satisfactory
results when you are not properly equipped in this
regard. The following styles of pliers are necessary in
adjusting spectacles: Snipe-nose (half round), full
round, concavo-convex, bridge angling, and stud pliers.
There are other styles that will facilitate the work, but
these just enumerated are absolutely needed.
37
38 THE MECHANICS OF FITTING GLASSES
Miieli practice will be re(|uired })efore you will be
able to do justice to a bridge iu the matter of bendiug, and
it is suggested that you make use of all available old
frames or even buy some cheap frames to practice
bending, etc.
Adjusting,
If the lenses are too high and it is desired to lower
them bend the shanks of the bridge downward, but re-
member that in doing this you will lower the angle of the
bridge and allowance must be made for this. If the lenses
are too low bend the shanks upward, remembering that
this will also alter the angle of the bridge.
The angle of the bridge may be varied by angling the
crest with ordinary snipe-nose pliers or by curving the
shanks upward or downward at the eyewire or strap, but
the best way is to use pliers that are especially made for
angling, for instance, the Berg pliers, by means of which
the angle can be changed properly in a very short time.
The shanks may be lengthened or shortened to con-
trol the distance of the lenses from the eyes by changing
the relative position of the point at which the bridge
curves to make the shanks. First, with a pair of snipe-
nose pliers flatten out the curve in the shank, then with
a pair of full round pliers put the bend in the bridge just
where you want the shanks to begin and continue to bend
the shanks over until they are brought into the proper
position. It is (piite essential that pliers with full round
jaws l)e employed for making these curves as the other
pliers will mark and cut the covering of the bridge.
T\\r pupillary width of the glasses should be con-
THE MECHANICS OF FITTING GLASSES 39
trolled l)y the direction taken by the shanks without dis-
turbing the width of the base of the bridge.
The width of the base should l)e altered l)y using
pliers that have one jaw concave and the other convex.
Changing the base will also affect the pniiillary width.
In bending a bridge it will be wisest to ascertain just ex-
actly what alterations are necessary before making any,
due to the fact that every dimension is dependent upon
the other and a change in one will cause a corresponding
change in some of the others.
To bend temples so as to angle the lenses or where
one ear is higher than the other and one temple must l)e
raised use two pairs of pliers; with stud-pliers grasp the
end-piece close to the edge of the lens or eyewire and with
a pair of snipe-nose pliers take hold of the outside end of
the end-piece and bend the part of the end-piece to which
the temple is attached so as to move the temple upward or
downward as may be desired; in other w^ords the end-
piece is slightly twisted. Above all things do not curve
or bend the temple itself, but confine your bending to the
end-piece.
To curve the temples for the turn of the ear use a
pencil or something else round and curl the temple as you
would a feather, by drawing the end of the temples be-
tween your thumb and the pencil. Temples may be curved
outward in a similar manner where they cut into the flesh
on the side of the face.
If you find one lens sits higher than the other it may
be that one ear is higher than the other and the trouble
should be rectified by angling the temples as already ex-
plained in next to the last paragraph.
How To Adjust Eyeglass
Mountings.
We shall consider here two kinds of eyeglass mount-
ings in general, that is, those of the tinger-pieee type and
those with the regular hoop springs. In differentiating
between these two kinds the spring of the regular and the
bridge of the finger-piece mounting are the essential
l)oints and the same rules wnll apply to both classes of
mountings except wliere they apply to these two conflict-
ing portions.
The first aim in fitting the eyeglass is to make it stay
on securely with comfort, and in effecting this we cannot
sacrifice correctness of position, so tliat many times we
are confronted with a complex problem when we endeavor
to make these three features work harmoniously. Let
us first reason out the proper means of holding the
mounting securely on the nose. Before we go farther
try this experiment and get it impressed firmly upon your
memory: Place the palms of your hands together and
administer a slight pressure; notice when you do this that
it requires considerable force to slide your hands a^iart.
Now place the backs of your hands together and observe
liow hard you have to press to make it difficult to slide
your hands on each other. Why is this so? It is so be-
cause in the case of your i)ahiis being laid together they
presented a multiplicity of contact points, one fitted
closelv into the other and they adhered to each otlier.
4U
THE MECHANICS OF FITTING GLASSES 41
Apply this same sort of thing to the eyeglass guard and
you have solved l)oth the pro])lein of holding the glasses
on securely and that of making it comfortahle.
The guards themselves must present a smooth sur-
face to the flesh and must be curved so as to conform to
the contour of the portion of the nose over which they
rest. To curve the guards in this manner it is quite es-
sential to have the proper kind of pliers ; the best for
this purpose are those that have one convex blade and
one concave so that by simply pressing the blades to-
gether the portion of the guard on which you are working
assumes a corresponding curvature in degree depending
on the amount of pressure you give the pliers. By using
pliers of this kind the guards may be accurately curved
without interfering in any way with the remainder of the
guard or its general angle, etc. Suppose now after you
have given the guards the proper curvature and granting
the other parts of the mounting are evenly balanced and
straight, that one lens is higher than the other. This is
a trying puzzle to every beginner and to many who have
been in the business a long time. We will say for instance
that the left lens is higher than the right. Take the
curved pliers and bend the bottom of the left guard out
slightly, being careful not to bend it so far that it leaves
the flesh. If this is not sufficient to lower the lens, bend
the entire guard on its axis so that the bottom portion
does not press so hard; this will bring the top of the
guard in tighter, but care must be exercised not to bring
this in too tight. Further lowering of the left may be
accomplished by raising the right lens, which is done by
bending the right guard in toward the nose slightly at
the bottom. It is surprising how bending of the guards
42 THE MECHANICS OF FITTING GLASSES
will t'lTcc't tlie respL'ctivo lici^vhts of the lenses. As was
said at the beginning security, comfort and correctness
of position must all obtain to tiie fullest possible degree
and one must not be sacriliced for the others.
In all cases the top of the guard should be curved out
slightly to agree with the curvature of the nose as it
merges into the ))rows, if this curving is not done here
the top of the guard will cut into the flesh and prove very
uncomfortable. Jt is the bottom of the guard that sup-
ports the weight of the glasses and the top that prevents
them from tilting over, so that the top of the guard must
necessarily press a trifle harder than the l)ottom, and as
a general thing more pressure can l)e stood here than
at the bottom because there is nearly always a little
cushion of flesh here. Wherever the guard rests on a
bony part of the nose the contact must be very even and
the pressure comparatively light, else the guard will cut
the skin. By giving the guards the same curve as the
nose they will stick to the skin and much less pressure
will be required than otherwise. Another good plan is
to bend the entire guard out from the back so that there
is more pressure along the front or outside edge of the
guard than in the back; this will cause the flesh to pile
up slightly, as it were, in front of the guard and form a
wedge of the flesh which prevents the mounting from
slipping forward.
In the case of a regular mounting with the hoop
spring sometimes it is desirable to have the spring tilting
slightly at the to]) away from the forehead on account
of licaxy lnows oi- high nose. There ai"e s])rings that
are made with this tilt but if the mounting you are ad-
justing is not tilting and you would pi'efer to have it so
THE MECHANIC'S OF FITTING GLASSES 43
you can very easily hciid it to liavc the desired tilt. To
do this nse ^Yllat is known as stud [(licrs, taking' tlieiu in
one hand and gripping- the straj) of one of the studs with
them. Grip the pUers tightly and with the thumb of your
other hand press against the top of tlie spring and you
will find that you can bend it outward. After doing this
take liold of the other stud with the pliers in a similar
way as before and repeat the operation on this side, thus
evening u}) the tilt from both sides. It will be w^ell to
practice this so that when >()U want to do it you are sure
that you know what you are doing and it will prove ({uite
valuable in getting a good tit many times, for often the
mounting cannot be set far enough back on the nose due
to protruding brows.
When placing eyeglasses on a patient's nose do not
hold the glasses by placing your fingers on the two sides
of the lenses, Init allow your fingers to touch only the
edges of the lenses. This keeps the lenses clean, elimi-
nates the possibility of sticking your finger in the pa-
tient's eye and is not so awkward as the other way.
In handling finger-piece mountings do not grasp the
finger-pieces with the thumb and forefinger, but use the
thumb and middle finger and press the forefinger against
the bridge; this steadies the mounting and gives you a
secure hold on it. Your patients should be instructed to
take hold of the mountings in the same manner.
If the guards are covered with shell, be sure to
smooth off the edges all around, using a fine, flat file for
the purpose. It w^ill often be found in cases w^here the
mounting is not comfortable and the guards are covered
with shell or a similar substance that the trouble can be
relieved by filing the edges of the shell on the guards.
44 THE MECHANICS OF FITTING GLASSES
Wheii mountings contain toric lenses the efficiency
of the lenses may be increased by bending the lenses in
toward the temples. This enables the patient to look
sideways without being annoyed by the edges of the
lenses.
One of the chief objections to finger-piece mountings
is that they are apt to sit too high and to sit farther from
the face at the bottom of the lenses than at the top.
Great care must be exercised to prevent these two con-
ditions and it will be well for you to understand how to
overcome these difficulties. The standing away from the
face at the bottom of the lenses can be rectified by spread-
ing the guards at the bottom and l)y making them incline
somewhat from the vertical. The custom of bending the
ends of the bridge downward and drilling the holes above
center is not advised in cases where it is desired to set
the lenses lower, because it spoils the appearance of the
mounting, narrows the base of the bridge and disrupts
the proper working of the springs and finger-pieces.
The better plan would be to fit mountings in which the
guard-arms are so constructed that the guards may be
raised without changing their angle or mountings that
are supplied with drop-studs or "tangent" studs, as they
are called by some. To increase the tension of springs
on finger-piece mountings detach the long end of the
spring, gripping it with a pair of pliers, and pull the
spring tighter on the coil. To decrease the tension push
back on the coil. In cases of springs of the lever variety
in which it is not possible to adjust the tension of the
coil, l)en(l the long i'vvo end; to increase the tension bend
it toward the side it presses, to decrease, press toward
the opposite side.
THE MECHANICS OF FITTING GJ.ASSES
4.-)
Pliers You Need.
Full Round.
Half Round (Snipe Nose).
Cutting.
Stud.
46 THE MECHANICS OF FITTING GLASSES
Angling.
Concavo-convex.
Strap.
How to Judge a Good Finger-
Piece Eyeglass Mounting.
The two main things for consideration are the
springs and the guards. There are, in general, three
kinds of springs — coil, lever, and ribbon or flat; these
are seen at times in combination and there are variations
of each kind. In the spring we look for constancy, dura-
bility, and strength. In other words the spring should
maintain an even pressure for a considerable time and
not be likely to come off easily. Coil springs are the ones
most likely to give trouble, especially if both ends are
attached to the mounting; if one end is left free there is
less likelihood of the spring playing out. Now then for
the guard : The requisite of a good guard is that it pre-
sent a smooth, flat surface to the flesh over a generous
space, for a guard will hold with much greater comfort
and less pressure if its powers of adhesion are well de-
veloped. To understand better just what is meant by
this place the palms of your hands together and see how
with a little pressure it is quite difficult to slide them on
each other; now place the backs of your hands together
and you will find that although you apply a great deal
of pressure you can slide them with ease. Guards that
are built like a crab's claw with twists and turns and
parts touching here and there are by no means efficient,
and there are many guards on the market just like this
47
48 THE MECHANICS OF FITTING GLASSES
— avoid lliciii if you want your ])ati('nts to wear the
glasses you give them with coinfort.
Another point for careful attention is the manner
in which the guard is attached to the mounting and range
of adjustments the general ('()ml)inaiioii offers. If the
guard is so attached that it cannot be moved higher or
lower and closer or farther away from the bridge and
the angle of the guard cannot be changed without inter-
fering with the workings of the spring, the mounting
should be discarded for one that does offer these neces-
sary adjustments. Most of the standard mountings can
be had in what is known as oft"set, inset, and extended
posts, so as to accommodate cases where the nose is ex-
ceptionally high or low or where the P. I), is wide and
the nose narrow; any mounting that cannot he had in
these styles is not a good one to adopt.
Right here it might be well to repeat that it is rec-
ommended that you adopt one or two good styles of tin-
ger-piece mountings, have a complete fitting set of each
and use these exclusively when fitting mountings of this
type, for if you have one or two good styles of mountings
and the full range of sizes from which to choose you will
be able to fit any case where it is at all possible to fit an
eyeglass. The fitting sets should be kept intact and com-
plete always and the mountings should contain lenses,
for w^ithout these it is difiicult to tell just how a mounting
will set and ))esides they offer a means indicating the dif-
ferent sizes of mountings by having the size of the mount-
ing <'t('h(Ml on them instead of having to use tags on the
mountings, which are constantly in the way and have a
very bad appearance.
How to Write Prescriptions
to Be Sent to the Shop.
This is one of the most important chapters in this
book and should receive very careful attention. A full
understanding of the connnon terms used in the optical
business and a knowledge of the construction of the vari-
ous kinds of lenses, frames, mountings and parts, etc., is
positively necessary, and it is just as essential to know
the common names for the various parts and operations
as it is to know of their construction, for without this you
will be unable to order and get just what you want. One
good plan is to take the general catalog of some standard
wholesale house and study it as you would one of your
most important text-books. If it were possible for you
to spend about two hours in the prescription department
of any wholesale optical house you would soon appreciate
the importance to you of knowing how to order so that
the man who fills the order will thoroughly understand
what you want without taking chances at guesses and
having to figure out some kind of enigma or some long-
winded description. Eemember that an order for a pair
of special lenses, for instance, has to pass through the
hands of several people, and if your orders are not clear
and concise each man has to waste a great deal of time
deciphering your specifications, thus delaying your work
and that of others. As far as possible in describing the
49
50 THE MECHANICS OF FITTING GLASSES
style of fraiiu's or iii()iiiitiii,<»s cataloii,' luuiihers should be
used. The followiiii;' is an exanii)le of a i)re8cription
received by a wholesale house fi'oin a man who thought he
knew all about oi)ties and fitting glasses and took offense
when corrected: The formulas for l)oth distance and
near were entered on the l)lank and this note appeared
below: "Put scales on the inside; but L do not want
bifocals." Another Kx gave the formulas for both dis-
tance and near without any explanation regarding what
kind of lenses were desired and the natural inference w^as
tliat bifocals were wanted, and so in accord with the cus-
tom the regular cement bifocals were supplied. From a
letter from this customer the house learned that he did
not want bifocals, but simply lenses for reading. But
how were they to know! It is really surprising how few
men know liow" to tell the wholesale house just what they
want, but it is just the people who do not know how to
order who experience the greatest trouble and delay and
who are the most unreasonable when they do not receive
what they tliought "the wholesale house surely ought to
know what they wanted, ' ' The instructions given in this
chapter refer mostly to orders sent in for filliuf/, records
having been discussed in another section.
Fundamental Rules.
Use a separate blank for each order or each pair of
glasses. Write clearly and avoid vague descriptions.
Nevei' use ink or indelible pencil to write prescrip-
tions that you send to the wholesale house foi- fiHing, as
this Rx accompanies the job in its journey through the
shop, and as water is used in grinding the lenses this
gets on Ihe pa[)er and runs the ink, making it illegible.
THE MECHANICS OF FITTIXC. GLASSES 51
When oi-deriii.i;- lenses he sure to state size oi' eye and
whether rimless or for I'lanies.
(rive each Kx a nuniher or i)atient's name and the
date.
Sign yonr name at the hottom. The iionse may rec-
ognize your handwriting, hut most likely not, for your Rx
is one among from 500 to 1,000 received daily.
Do not write instructions across ])rinted matter, as
this makes tliem very diftieult to read.
Name or Number.
It is well to give each order a name or number, which
will be useful when writing about an order or for other
future reference.
Formulas of Lenses.
When the usual form is followed of writing the
sphere first, the cylindrical value next, and the axis of
cylinder next, it is not necessary to append the abbrevia-
tions "Sph.," "C'yl.," or "axis," even when not written
on a tabulated blank, in which case the form should be
thus : — 1.50 — .75 X 90.
When distance lenses only or reading lenses only are
wanted give the formula for the particular correction you
want and not both. When both formulas are given, as
in cases where bifocals are desired, it is best to give the
total reading correction in full and not the addition for
the bifocal portion. In such cases where the addition is
given you must be very particular to append the word
"Add" after the amount to be added. It is because it is
so easy to forget to affix this little word that it is much
52 THE MECHANICS OP^ KITTING GLASSES
bettor to always "ivc tlio full reading eorreetion after
the addition lias l)eeii made; get into tlie habit of doing
this and yon will avoid many mistakes and misunder-
standings.
Other Lens Specifications.
Always state whether yon want "toric" or "flat"
lenses. While, sti'ietly speaking, there is no such thing
as a "spherieal toric," the correct term being "menis-
cns," the term "toric" is generally accepted as applying
to all lenses constrncted on a deep periscopic base. By
"flat" lenses is meant all lenses that are not toric (or
meniscus).
Give the "size of eye" in the proper space; this is
the size of lens as has been described in another part of
this book.
When lenses only are being ordered and you do not
want them put into a frame or mounting, be sure to
state whether they are to l)e rimless or inserts (for rims),
and if rimless how many holes you want drilled in them.
In specifying for the drilling of holes always specify the
number of holes i)er pair, even in cases where only one
lens is ordered.
Should you ordei- just a single lens and do not send
the other lens to be matched for thickness, be sure to give
the thickness of the lens at the "strap," or, in other
words, where it is attached to the mounting. This thick-
ness may l)e ascertained by measuring with a millimeter
rule oi' l)y using a sti'aj) gauge.
if you do not gixc any instructions regarding how the
holes shall be di-illcd tlicy will be drilled "on line"; in
cases where von want ilic lenses to set lower when usinsr
THE MErHAXICS OF FITTING GLASSES
53
eyeglass moimtiiii's, si.ecit'y that you want the holes
drilled above center, stating how ninch, thus: Drill one-
eighth al)Ove, or drill one-sixteenth ahove, as the ease
Tuay I'eiiiiire.
The Frame or Mounting.
Know just what you want heiv and give six'cifie in-
structions, for tliis part of the order is just as important
as that part which refers to the lenses; renienil)er the
man who fills your order does not see the patient and
must have definite dimensions l)y wliich to he guided if
he is to make up a frame or mounting that will fit.
Eyeglasses.
In the proper space state what style of mounting you
desii-e and what kind of material you want, such as gold
filled, solid gold, nickel, etc. As far as possible it is well
to give catalog or stock nimibers becanse these are qnickly
reiCd and nnderstood, save space on the order blank and
save time in the shop. AVhen ordering finger-piece
mountings remember that the numbers given in your fit-
ting set refer to size of the bridge only and not to the
particular style of mounting. For instance, let us say
you are fitting from a set of mountings known as the
"-Stavthere Mountings," and you decide that a No. 842
is the size vou desire and the patient orders gold filled,
on vour order you would specify -G. F. Stay there 842."
Thus vou cover every point of style wanted, so that the
man wdio fills your order knows positively just what you
want. Figure out exactly what size lenses you want; do
not give the pupillary distance and the bridge number
amrexpect the workman to figure out the size lens re-
54 THE MECHANICS OF FITTING GLASSES
quired, because while it would he possil)le for him to do
this, remember tliat th.^ man who grinds the lenses does
not i)iek out the mounting or adjust it to the lenses, and
the preserijjtion clerk has t(» figure it out and mark it on
the order before it goes into the shop, and probal)ly
rather than delay the other orders that are all properly
written he will lay your order to one side until the others
are passed into the shop, thus delaying the filling of your
order. It will take you but a moment to decide what size
lenses you need and to mark it down on the order, so
in your own interest do this. Rememl)er that UOO eye size
is just one millimeter longer than (ID eye, and that 00 eye
is just one millimeter longer than eye, and each change
of eye size will make just one millimeter difference in
the pupillary width of the glasses. Tn ordering eye-
glasses of the finger-piece type the only data necessary
are :
Material, Style, Size of Mounting and Size of Lenses.
Pupillary width and "Spread of Guards" are superfluous
when ordering any kind of eyeglass mountings or frames,
because the pupillary width will l)e controlled by the size
of lens and size of mounting, and the "Spread of Guards"
will have to be effected by you when you fit the mounting
to the patient's face, for eyeglass guards cannot be
adjusted "by mail"; the i)atient must be right in front
of you at the time.
]\Iost of the foi-egoing applies to finger-piece mount-
ings; hooi) spring mountings must l)e oi-dered in a some-
what different manner. Give the kind of material, size
of lenses, size and style of stnds, style of guards, size
and style of sjjring. This iiif'oi-mat ion definitely stated
will get you Just exactly what you want.
THE MECHANICS OF FITTING GLASSES
Specimen of the Usual Form of Rx Blank Supplied by
Wholesale Optical Houses, Containing an
Order for Spectacles.
42^
PATIENT
B
NO.
SPH. j CYL. 1 AXIS 1 PRISM
BASE
LERS INtTRUCTIOIIS
w - ^/
h .p^s^ <90
l\ --h/.
f-.^^a /ySX)
(3)- -
MARK A CIRCLE AROUND STYLE WANTED AS INDICATED BELOW .
DRILLING
KRYPTOK 1 PERFECTION
BIFOCAL 1 BIFOCAL
^
^"^ pE^Tr-^r
PER PAIR
ibovt Ctntir BelowCinlir
FRAME INSTRUCTIONS;
-^/:i<=) -/o/^.
IV^EVE ooo
BRIDGE
NUMBER
PUPILLARY X, •^
DISTANCE %£/ C/
s
BRIDGE J
HEIGHT
POSITION OF CREST
AngleofCrest
WIDTH AT BASE
U J
z u
<
*?
.—
""
y^Xf
/
'h
^
^h
_ -sr
^h
_ w
1
=-
.h
E
-- ,,
_CVJ
TT^
"!-'
— -^
= S
— s
^
— 3
-^
2 Holes Per pair "1 16 above line.
3 Holes Per Pair "on line.
4 Holes Per Pair "on line.
Ascertaining the Power of
L
enses.
There are two ways in which to find the power of a
lens, viz., by using a lens measure and by neutralization.
The lens measure (see illustration) is about the size of a
man's watch and resembles it somewhat in general shape.
At one side there are three short pointed rods, the cen-
ter one being moval)le in the manner of a plunger, and the
other two stationary. By depressing the central rod a
corresponding movement will be noticed in the hand that
operates over the dial. When all three rods are of e(|ual
length the dial will indicate zero; when the central rod is
depressed below this level the hand will indicate plus
powers on the dial, and when the central rod is allowed
to protrude further than the other two the hand will
stand over numbers on the dial indicating minus powers.
To measure the power of a lens the lens should be held
in one hand and the lens measure in the other with the
dial in full view; press the points of the measure against
one face, rotate the lens so that the points pass over
several meridians of the lens and note whether the read-
ing of the dial changes as the measure is placed over dif-
ferent meridians of the lens. If it remains constant the
surface is a spherical one ; now do the same thing on the
other side of the lens, and if you determine both sides to
])e spherical, algebraicly add the two readings and you
have the power of the lens. For instance, suppose one
59
60
THE MECHANICS OF FITTING GLASSES
side of the lens is phis '2.00 (li()i)ters and the other side
is niinns 1.25, tlien the h'lis is a phis .75 D. If one side
should he plus l.(H) and the other i)lns 1.50, then the lens
would lia\e the ])ower of plus 2.50 1).
Now snppose wlien you i-otate the lens the measure
shows a varvino' power over its surface, then there is
indication of the i)resence of a cylindrical power. In
Lens MeasLire.
reg'ulai- (not toric) lenses one uiei-idian of such a surface
would indicate zero on the dial and the opposite meridian
would iiivc the power of the cylinder; the axis of this
c\ linder would, of course, he where the readiny^ is zero.
If the lens is a sj)hero-cy linder one side will show the
sphere and llic other llie cxlindei'. Toric lenses are meas-
ui-ed in llic same \va\\ except Hint in iiieasui-iui;- the cvlin-
dei- it must he i-euienihered that there is hoth a spherical
and a cylin-lrical power on one side. For instance, if a
THE MECHANICS OF FITTIXC GLASSES
(il
toric Ions is i>TOun(l on n pins (i D. base and contains a
oylindrical lunver ol" pins l.dO D. this side will slu.w pins
(/in one moridian (tiic axis ol' tiio cylinder) and pins 7
in the opposite niei-ili the lens it shows no
power. The opposite of the trial k'lises used for this
pnri)()S(' will he tlic power of llic lens. In other words,
to neutralize take lenses of the coiicsponding- o])posite
j)ower — plus to neutralize minus and vice versa. Ke-
meniber when looking through a plus lens and moving it
Stoco Lens Centering and Axis Finding Instrument.
from side to side that things viewed will ai)[)ear to move
opposite to the direction in which the lens is moved, and
when looking thiough a minns lens things will ai)pear to
move in the same direction in which the lens is moved,
and that when the zero is reached no movement will be
discernible. Tn placing cylinders over the lens the power
^vill be the o|)posite ol" the test lens, but the axis will be
the same as that indicated b\- the test lens.
THE MECHANICS OF FITTINCI GLASSES
£3
Tn these two tests the lens iiieasiu-c if i)i-(.perly ad-
justed will l)e reasonably acenrate, hnt when absolute pre-
cision is deiuanihMl the process of neutralization must be
employed. It will l)e found advantageous to use the lens
measure first and then the test lens for neutralizing, as
the lens measure will show ai^proximate results and
having used it first will save niucli time in s<'le('ting the-
))r()per lenses for the neutralizing.
A. O. Co. Centering and Axis Finding Instrument.
Having determined the focal power of the lens it is
alwavs well to make a test to see whether the lens con-
tains a i)rismatic power. To locate the presence of a
prism proceed as follows: Look thi-ough the lens at a
vertical straight line on the wall or drawn on a piece of
paper. Hold the lens at such a distance from this line
that it is clearly visil)le ; in cases of high power lenses it
will be necessary to approach (piite close to the line.
Hold the lens so that its DOtli meridian is absolutely
vertical and move it over the line so that the lens is cen-
tered over it and notice whether the portion of the line
64
THE MECHANICS OF FITTINO GLASSES
that is viewed tliroiigh the lens is a direct continuation of
the line viewed outside of the lens; in other words, note
whether there is a displacement of the line to one side or
the other of the ends of the line thai aii[»r()a('h the two
sides of the lens. If the line is continiious without dis-
lilacciiiciit there is no prismatic ]h)W(M' in the lens, hnt if
Lloyd Axometer.
there is a displacement there is a prism there. The apex
of the prism will be in the direction the line is displaced.
There are two ways of measuring the ])Ower of the prism:
Charts are made to hang on the wall which indicate the
power of the prism liy the amount of displacement and
there are nu'chanical prism measures for the purpose.
To Ascertain the Position of the Plus and
the Minus CyHnder in a Compound
Lens by Simple Inspection.
You may pick up a lens that is a spliero-cylinder aud
see that the cylinder is present and by rotating the lens
tell when you liave the two principal axes, but there are
few who know the following simple truth: When a
sphero-cylinder is rotated on its optical center objects
viewed through it will appear to move against the move-
ment of the lens at the axis of a plus cylinder and with
at the axis of a minus cylinder. Thus a lens of the power
+ 50 Sph. + 50 Cyl. axis 90, will show an against move-
Card Protractor.
66
THE MECHANICS OF FITTING GLASSES
meiit wlieii rotated across the !)l)tli meridian and a with
movement when rotated across the ISOth meridian.
Knowing this will enal)h' you to (inickly a|)proximate the
power of a lens and to know exactly which is the principal
meridian when ])lns cylinders are reckoned on and which
is the i)rinci})al meridian when minus cylinders are
considered.
Colmascope.
THE MECHANICS OF FITTING GLASSES
67
Kryptoscope.
The Colmascope, shown on Page 66, and the Kryp-
toscope on this page are instruments used for detecting
strain and striae in mounted rimless lenses.
Simple Method of Measur-
ing Prismatic Power
iR a Lens.
It very often occurs that a lens containing a prism is
bronglit to yon for dnplication and nnless yon have some
means of detecting- the presence as well as the power of
the prism yon will dnplicate many lenses incorrectly. A
simple bnt remarkal)ly accnrate prism measuring device
may be made as follows :
On a strip of paper al)ont 15 inches in length draw a
vertical line al)ont fonr inches long close to the left hand
edge of the paper ; at the top of and perpendicular to this
upright line draw a horizontal line to run the length of
the paper. Starting one inch to the right of the vertical
line draw other vertical lines about two inches high
upward from the horizontal line, all just one inch apart,
until you come to the end of the horizontal line. Num-
ber the vertical lines consecutively, calling the first line
at the left, which runs down from the horizontal, Zero,
and the next line to the right, which runs upward, No. 1.
These figures should be about one-half an inch high and
should be distinctly made, so as to be visible at a dist-
ance of nine feet. When tlie chart is complete, i)lace it
on the wall and stand just nine feet froiii it wlii'ii neu-
68
THE MECHANICS OF FITTING GLASSES
69
tralizing lenses. Wy holding a lens np so tliat the zero
line runs through the physical center of the lens and
noting the amount of displacement as viewed through
the lens and observing the number on the chart to which
the zero line is displaced, you will have a very accurate
indication of the power of the prism. The base of the
prism will be just opposite to direction of the displace-
ment. The quickest and easiest way to understand this
will be to construct a chart and try the method suggested
with a prism from your trial case.
A Mechanical Prism Measure.
A Method for Simplifying
Transpositions.
The rules we have for the transposition of lens val-
ues are so long and complicated that there are very few
who memorize them and it frequently occurs that just
when we want to transpose is just the time we are in a
hurry or need to Imow right away and cannot recall or
find the rule to fit the case.
To simplify this and to show you how you can have
the rule you want always at your finger tips, we have
evolved a few simple rules.
First of all, to eliminate the constant reference to
changing signs let us employ the algebraic method of
combining quantities, which is the same as the arithmetic
or common way when adding plus to plus or minus to
minus, but when combining plus and minus we take the
difference and use the sign of the larger number. For
instance, +3 added to — 2 equals +1. In subtracting
algebraically we always change the sign of the number
subtracted and then proceed as in addition. Examples:
+3 subtracted from +4 is the same as — 3 added to +4
which equals +1. — 2 subtracted from — i is the same
as +2 added to —4 which equals ^2.. — 1 sul)tracted
from — 3 is tlie same as +1 added to — 3 which eipials — 2.
Bv usinii' this method we are able to I'csolvc nil the
70
THE MECHANICS OF FITTING GI-ASSES 71
rules for the transposition of spliero-cylindors into one
simple rule :
To transpose spliero-cylinders always add the sphere
xo the cylinder (algebraically) for the new sphere, the
power of the cylinder remains the same, but change its
sign and use the opposite axis.
Examples :
+3 +1 Ax 90 = +4 —1 Ax 180
—2 +1 Ax 90 = —1 —1 Ax 180
+1 —2 Ax 90 = —1 +2 Ax 180
It all simplifies itself when you remember that add-
ing +1 to — 2 equals — 1. By a thorough understading
of this basic truth and remembering to always add you
will have the method firmly fixed in your mind and will
not have to memorize a complicated set of rules or even
one rule.
In combining two cylinders we pursue just the oppo-
site course from that for sphero-cylinders, in that instead
of adding we always subtract. Suppose we have the two
cylinders +1-00 ax 180 and -f 3.00 ax 90 which we wish to
combine in a sphero-cylinder form, the result is -f 1.00
-f 2.00 ax 90.
The rule for combining cylinders is :
Take the power of the first cylinder for the sphere;
subtract (algebraically) the first cylinder from the sec-
ond for the new cylinder and use the same axis as that of
the second original cylinder. Examples :
—1 Ax 90 and +2 Ax 180 = —1 +3 Ax 180
or +2 —3 Ax 90
Also
—4 Ax 90 and —2 Ax 180 = —4 +2 Ax 180
or —2 —2 Ax 90
72 THE MECHANICS OF FITTING GLASSES
To reduce a sphero-cylincler to two cylinders we do
just the reverse of the a])ove. The rule is : For the first
new cylinder add (algebraically) the sphere and original
cylinder and use the same axis ; for the second new cylin-
der use the original sphere with same sign and an axis
opposite to that in the original compound.
Examples :
+1 +2 Ax 90 = +3 Ax 90 and +1 Ax 180
Also:
—2 —2 Ax 90 = —4 Ax 90 and —2 Ax 180
Likewise :
—1 +3 Ax 180 = +2 Ax 180 and —1 Ax 90
Decent ering Lenses for Prism
Val
ues.
The base upon which these fonimlas have been con-
structed is the simple fact that a 1 diopter lens decentered
9.4 millimeters will have a prism power of 1 degree.
Formulas :
9.4 X Prism
= Decentration.
Lens
Lens X Decentration
= Prism
9.4
From which we have the following rules:
To find the amount of decentration (in m.m.) needed:
Multiply 9.4 by the strength of the prism in degrees and
divide by the strength of the lens in diopters.
To find the strength of prisut (in degrees) for a cer-
tain decentration: ^lultiply the power of the lens in diop-
ters by the amount of decentration in millimeters and
divide by 9.4.
These rules apply to both convex and concave lenses,
but it must l)e remembered that the base of prism will
be opposite in plus and minus lenses. Another point for
emphasis is in determining the amount of prism or de-
centration in sphero-cylindrical lenses the dioptric power
in the meridian of decentration is the value to be used in
making these computations.
73
Estimating the Power of
Lenses with Calipers.
Taking the glass ordinarily used in the manufacture
of lenses, it is possible to estimate the power of a lens by
the difference in thickness of the periphery of the lens
as compared with the thickness at the center. Suppose
the lens is 40 millimeters in diameter, then a difference
in thickness of two-fifths of a millimeter means that the
lens is one diopter, or if the lens is not so wide as this the
proper deductions must be made accordingly. For in-
stance, suppose the thickness at the center, as measured
with calipers, is 2 mm. and the thickness at a point 10
mm. from the thickest point is 2 4-5 mm., this would
mean that the lens is minus 4 D., for at 10 mm., which is
the radius corresponding with a diameter of 20 mm., 1-5
mm. difference in thickness would correspond to 1 D., and
since the difference in this case is 4-5 mm., the lens must
be 4 1)., and since the center is thinner than the periphery,
it must be a minus lens. When we consider the exactness
of some of the calipers that are made, it is easy to see
how, by this method, a very close approximation to the
actual power of a lens may l)e made.
What to Do (or Loose
Screws.
By loose screws in this sense is meant screws that
require frequent tightening and which appear to refuse
to stay tightened.
Screws may be chronically loose for several reasons,
principal of which are stripped threads, enlarged hole or
a screw that is not designed for the particular threads of
the straps.
If the threads are stripped on the screw the remedy,
of course, is a new screw, but if the threads are stripped
in the straps another plan must be followed which will
also apply to cases in which the hole has become some-
what enlarged. Provide yourself with what is known
as a repair screw tap which differs from the ordinary
screw tap in that it is a trifle thicker, its purpose being
to make new threads in a hole slightly larger than the
regular size. Take out the old screw and the lens and
turn the repair tap in the hole until it projects from the
other side of the straps. Now you will need what is called
a repair glass screw, a screw that is somewhat larger
than the usual size glass screw. A supply of repair glass
screws should always be kept on hand for just these
cases.
Should you have a steel screw that you can't keep
tight and cannot duplicate, it can be tightened once for all
75
76 THE MECHANICS OF FITTING GI ASSES
by dipping in cyanide of potassium or anytliiiig else tiiat
will cause rust to form and then replacing it in the
mounting. To remove such a screw all that is necessary
is after having removed the lenses to heat the part con-
taining the screw to a high temperature and to pack
bees' wax around this part and let it stay this way for a
few minutes; the wax will melt and run in around the
screw and cut the rust and the screw can be turned in
the threads just the same as when it was first put in.
How to Mount Rimless
Lenses.
The first requisite in the successful mounting of
lenses is to have the proper tools. In addition to a good
screwdriver and strap bending pliers it is necessary to
have a screw tap and a rat-tail file.
A screw driver should be selected that is short
enough to permit the top of it to rest in the palm of the
hand and this top should be revolving so as to allow the
driver to be turned without your losing a purchase on it.
It is a very common occurrence to see someone who is
putting a screw into a pair of glasses holding a screw
driver by the first three fingers and the screw driver
pointing upward past the forefinger. This is a ques-
tionable method, for it is too easy to let the screw driver
slip when held in this position and you do not have a good
hold on the screw itself. Some prefer to pick up and in-
sert screws with a pair of tweezers, but while at times it
is advantageous to use tweezers usually after a little
practice it is found surer and quicker to pick up and
insert screws with the thumb and forefinger.
The secret of mounting rimless lenses properly lies
in having the straps of the mounting lying flat on the
lenses, and in having the three holes— the one in the lens
and the two in the straps— in perfect alignment both in
regard to being one right over the other and in being
77
78 THE MECHANICS OF FITTING GLASSES.
parallel so that the threads in the two straps will coin-
cide with the threads of the screw.
Tlie first step is to arrange the straps so that they
will lie flatly on the lens and so that the distance between
them will correspond to the thickness of the lens. To
accomplish this it is necessary in most cases to bend the
straps slightly closer together or farther apart. This
bending of the straps can be done with ordinary snipe-
nose pliers but it is best to use strap pliers that are
especially designed for this purpose, for by using these
strap Pliers.
special pliers the bending and paralleling of the straps
can be done all at the same time without likelihood of
breaking the straps.
Having the straps properly bent, the next step is
to insert the lens between them and to try the holes
through the straps and lens with a screw tap to make
sure that all three holes are in line and the threads on
the straps will take the screw without forcing. In trying
the threads with the screw tap turn the tap a few times
in the hole (with the lens in the straps) until the end of
the screw tap projects slightly through the other side like
a screw would do. If you find the tap turns without re-
THE MECHANICS OF FITTING GLASSES. 79
quiring much force or without binding, you may insert
the screw and turn it down, but if the tap binds in the
threads it indicates either that the sides of the straps are
not parallel or else the hole in the lens does not center
properly over the holes in the straps or perhaps both con-
ditions exist. If the hole in the lens does not line up
properly with the holes in the straps, ascertain by in-
spection where the lens hole binds on the screw tap and
which way the lens needs to be moved or the hole needs
to be enlarged so as to admit the screw without pressing
against the glass. Often it will be found possible to move
the lens in the proper direction by bending the edge
straps down, on the lens or away from it. By "edge
straps" is meant the upright straps that press against
the edges of the lenses. These edge straps should be
bent so that they lay firmly against the edge of the lens,
following its contour as closely as possible. If it is not
found possible to line up the hole in the lens by moving
the entire lens and adjusting the straps then the hole
must be enlarged at the place where it binds on the
screw, but this should be the last resort as a hole that
is larger than necessary will cause the lens to loosen
easily and to require frequent tightening of the screw.
To enlarge the hole use a round rat-tail file. Moisten
the file slightly and having inserted it in the hole file
against the glass where the screw binds. Usually a little
filing will suffice and it is better to make the screw tap
test after one or two strokes of the file than run the risk
of filing away too much glass.
When the holes are properly aligned and the straps
correctly adjusted insert the screw and turn it down
firmly but if you find it binds even a trifle take the lens
80 THE MECHANICS OF FITTING GLASSES
out aud endeavor to discover the cause, for while you
may be successful in g-etting the screw all the way in
without breaking the lens if it binds at any point the
lens will crack "all by itself" as your patients will tell
you, within a few hours or perhaps a day or so after you
mounted it.
The proper way to hold a mounting and the lens you
are setting up is to place your forefinger under the strap
and lens and your thumb on top of the mounting, in other
words, hold the mounting in your hand with your finger
right under the strap that the screw last goes through
and if the straps are properly bent the combined pressure
of the straps and your finger will be sufficient to hold the
lens in position.
After the screw is in place the pointed end should be
cut oft' with cutting pliers close to the strap. If end-cut-
ting i^liers are used you will usually get a clean cut, but
if you use side-cutting pliers it will be necessary to
smooth oft" the end of the screw with a fine flat file, and
in doing this care must be exercised not to file away the
surface of the straps, for if the latter is gold filled filing
its surface will expose the base metal and that portion of
the strap will be likely to corrode.
In summing up the mounting of rimless lenses just
one point must be emphasized: It is not hard if you
reason it out and above all things do not force a screw,
remembering that if yon have to force it there is indica-
tion that it binds somewhere, most probably against the
glass and the lens will break at the first jar and you will
have what is known as a "screw-crack" or a lens that
broke mysteriously.
Record Systems (or the
Refractionist.
One of the most important departments in the busi-
ness of the refractionist is the records, and it will be well
worth the time required to study into this matter.
In the first i3lace, the records must be in such shape
that they will offer the greatest convenience and sim-
plicity when it is found necessary to consult them. In
installing a record system this is one of the very first
things to be considered, because the reason you keep
records is that you want the information for future refer-
ence and you want to obtain it accurately and quickly.
There are two general forms of record keeping ; one
is the book in which the leaves are permanently bound,
and the other is the loose-leaf or card-index system.
Both of these have their respective advantages and dis-
advantages. The bound book is secure and pages cannot
be lost out of it without l^eing torn out ; at the same time
it is rather bulky and much space must be kept idle for
considerable time if it is desired to keep the full history
of a case together and when the full history cannot be
kept together conditions become complicated and there is
likelihood of error or else much additional work in mak-
ing notations on every record, necessitating a long search
when a case is to be traced. The only objection to the
81
82 THE MECHANICS OF FITTING GLASSES
card system, is that cards may be mislaid or lost, but this
ditficulty can be easily overcome.
The writer is very decidedly of the opinion that the
loose-leaf or card index systems are the most satisfactory
and efficient. Some find it convenient to combine the
loose-leaf and card-index systems, by using light weight
cards in a loose-leaf binder and when these records are no
longer needed for immediate reference to remove such
cards and place them in a filing cabinet or drawer espe-
cially made for the purpose. Others find it more con-
venient to use loose cards and when the record is com-
plete, and the prescription has been transferred to an
order blank for transmission to the manufacturing opti-
cian, the record card is placed in the filing cabinet at once.
This is simply a matter of detail and can be arranged
to your own preference without materially affecting the
system in general as recommended in this article.
Cards for this purpose, already printed, may be
bought, but in the long run it may prove more economical
to have the cards especially printed to meet A'our own
particular requirements. Every man has different ideas
in regard to what he wants recorded and it is these little
details that make the stock printed cards unsatisfactory.
There are certain things, however, that all cards must
show, and they are as follows :
The patient's name, address and age.
The date (this is of utmost importance).
The formula for the lenses prescribed to be worn
(both the distance and near correction should be given).
The frame nicasurements.
The kind of glasses supplied on the original order
and the price.
THE MECHANICS OP FITTING GLASSES
83
The following- infoniiation will prove of value:
The patient's complaint when coming to yon for
treatment or glasses and a description of any peculiari-
ties not shown by the refraction record.
The patient's occupation.
The formula of the lenses previously worn.
The result of the retinoscopic test.
The patient's full correction (this often will differ
from what you prescril:)e to l)e worn).
The condition of the extrinsic muscles.
Did the patient come to you through an advertise-
ment, or recommendation of a friend — if so, the name of
same.
Having completed such a record, should the patient
return at some later date and you find the condition of
the eyes to be different, a new card should be made out
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and attached to the front of the old card, and a notation
should l)e made on the old card showing that a new pre-
scription has been written.
A portion of the card, usually on the reverse side
should be reserved for a record of l)usiness transactions
84 THE MECHANICS OF FITTING GLASSES
with tlio ])ati(Mit. For instance, suppose ^Ir. Lynn i\
Doyle slumld jnociire a pair of glasses from you on Jan-
uary loth and on May 1st he breaks a lens in the glasses
he uses for distant vision, and come to you to have it re-
placed. You have classified and indexed the drawer that
contains the cards so that all you have to do is to look
under the Letter D and find Mr. Doyle's card. This will
show exactly what his lenses should he and all doubt in
this regard is eliminated. Here is where the extra space
will be of use: enter here something like this: "May 1,
1915, one right lens (D. V.), $2.00." The next time he
comes in for a rei)air, or to have a lens replaced, make an
entry on the card showing the date, what he got and what
the price was. This method will be of value in two ways;
it will obviate the possil)ility of doubt or controversy re-
garding the price and >ou will have a detailed record of
just how much business he does with you and at any time
you can run through your cards and ascertain just how
much business you have done during a specified period.
It will also prove advantageous where there are niore
persons than one in your office to use the records.
INDEX
Page.
Adjusting eyeglasses 40
Adjusting spectacles 37
Angle of l)ridge 28
Axis finders ;ii(ii^>;'