.


© 2015 Journal of Neurosciences in Rural Practice | Published by Wolters Kluwer ‑ Medknow 625

Sir,
We have read with interest the article of Mojumder 
et al. on the use of pupil to limbus ratio to measure 
anisocoria[1] and we would like to share our experience 
on this topic:

Some studies have demonstrated that digital photography 
is a very convenient tool for the measurement of pupil 
diameter in ophthalmic practice. It offers several 
advantages over other methods (inexpensive, accurate, 
more repeatable than other techniques, provides long 
lasting documentation, and eases masked observations).[2] 
However to take absolute measures of pupil diameter, a 
ruler or a template should be included in the photo, and 
care should be taken to its placement and orientation to 
avoid parallax effects. Otherwise, only relative measures 
of pupil diameter can be taken. Using relative measures 
of pupil diameter (pupil to limbus ratio), simplifies 
the process of taking the photos (it is not necessary to 
include extra elements in the picture) and could have 
important advantages over using absolute measurements 
in different situations:
• Intra-subject comparisons: This method is 

impeccable to monitor changes on pupil 
diameter on the same subject. As Mojumder et al. 
demonstrate in their article, this is a really 
convenient approach to monitoring pupil changes 
in the UCI. It can also be useful in the differential 
diagnosis of anisocoria (to monitor pupil change 
when apraclonidine, cocaine, or pilocarpine 
0.125 tests are performed)

• Inter-subject comparisons: To compare pupil 
diameters among different subjects this method 
h a s  a l s o  i m p o r t a n t  a d va n t a g e s  o v e r  t h e 
methods that use absolute measurements. Pupil 
diameter is correlated with limbus diameter. 
A 6-mm-pupil is probably maximum mydriasis 
in a subject with 8-mm-corneas, but it is not 
c e r t a i n l y  m a x i m u m  m y d r i a s i s  i n  a  s u b j e c t 
w i t h  1 3 - m m - d i a m e t e r- c o r n e a s .  I n  t h e  f i r s t 
case, pupil diameter is 75% of the maximum 

p u p i l  d i a m e t e r  w h e r e a s  i n  t h e  s e c o n d  c a s e 
pupil diameter is 46% of the maximum pupil 
diameter

• Defining anisocoria: Expressing pupil diameter as 
a percentage of limbal diameter makes possible 
a more logical definition of anisocoria. As pupil 
diameter has a wide distribution (young myopic 
subjects have bigger pupils than old hyperopic 
subjects),[3] we find the classical definition of 
anisocoria very rigid. A 0.5 mm difference should 
be considered significant in a subject with 2.5 mm 
pupils, but it is probably insignificant in a patient 
with 6-mm-pupils

• Comparing photopic and scotopic pupils in the 
same subject: In our experience, using absolute 
measures, anisocoria tends to be greater under 
scotopic conditions (not only on Horner syndrome, 
also in physiologic anisocoria and anisocoria 
related to parasympathetic lesions). This fact 
is probably due to bigger scotopic pupils. This 
bias could be avoided using the relative change 
in a pupil to limbus ratio between photopic and 
scotopic pupil.

In summary, we agree with the authors. Pupil to limbus 
ratio is not only a very convenient method to measure 
pupils. It also has many conceptual advantages.

Financial support and sponsorship
Nil.

Conflicts of interest
There are no conflicts of interest.

Julio González Martín‑Moro1,2, Belén Pilo de la Fuente3, 
Fernando Gomez Sanz1,4

1Department of Ophthalmology, University Hospital of Henares, 
2Department of Medicine, Francisco de Vitoria University, 
3Department of Neurology, University Hospital of Getafe, 

4Department of Optics II, Complutense School of Optometry,  
Madrid, Spain

Address for correspondence:  
Dr. Julio González Martín‑Moro,  

Department of Ophthalmology, University  
Hospital of Henares, Madrid, Spain,  

Department of Medicine,  
Francisco de Vitoria University, Madrid, Spain.  

E‑mail: juliogazpeitia@gmail.com

References

1. Mojumder DK, Patel S, Nugent K, Detoledo J, Kim J, Dar N, et al. Pupil 
to limbus ratio: Introducing a simple objective measure using two-box 

L e t t e r s  t o  t h e  E d i t o r

Conceptual advantages 
of using pupil to limbus 
ratio over absolute pupil 
diameter

Published online: 2019-09-26



626 Journal of Neurosciences in Rural Practice | October ‑ December 2015 | Vol 6 | Issue 4

Letters to the Editor

method for measuring early anisocoria and progress of  pupillary change 
in the ICU. J Neurosci Rural Pract 2015;6:208-15.

2. Twa MD, Bailey MD, Hayes J, Bullimore M. Estimation of  pupil size by 
digital photography. J Cataract Refract Surg 2004;30:381-9.

3. Hashemi H, Yazdani K, Khabazkhoob M, Mehravaran S, Mohammad K, 
Fotouhi A. Distribution of  photopic pupil diameter in the Tehran eye 
study. Curr Eye Res 2009;34:378-85.

How to cite this article: Martín-Moro JG, de la Fuente BP, Sanz FG. 
Conceptual advantages of using pupil to limbus ratio over absolute 
pupil diameter. J Neurosci Rural Pract 2015;6:625-6.

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Commons Attribution-NonCommercial-ShareAlike 3.0 License, which allows 
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DOI:  
10.4103/0976-3147.169772

Necessity of globally 
implementing the 
comprehensive 
mental health action 
plan: World Health 
Organization
Sir,
For decades, mental well-being has been acknowledged 
as an integral component of health.[1] In fact, a sound 
state of mental health can enable people to realize their 
potential, successfully deal with the stresses of life, 
work in a productive manner and thus contribute to 
the welfare of society.[1,2] Realizing the global impact of 
mental illnesses, its influence on other health dimensions 
and quality of life, the World Health Organization called 
for the need of a comprehensive, multi-sectoral response 
from health and allied sectors.[3]

Subsequently, in 2013 a comprehensive mental health 
action plan 2013–2020 was launched after consulting 
with stakeholders (viz., policy makers, specialists, health 
professionals, family members of a mentally-ill person, 
etc.,) to ensure promotion of mental health, prevention 
and prompt treatment of mental illnesses, and provision 
of rehabilitation and care services.[2] This action plan 
was proposed with four basic objectives, namely to 
strengthen effective leadership activities in mental 
health; to ensure the provision of holistic, integrated 
mental health/social care services in community settings; 
to implement strategies for promotion and prevention of 
mental health; and to strengthen information systems, 
evidence and research in the area of mental health.[2,4,5]

However, the recent estimates present quite a dismal 
picture as almost one out of every ten people globally have 
some mental illness, whereas only 1% of health personnel 
are working in the field of mental health.[6] It means that 
a large number of people who are actually suffering from 
mental illnesses are devoid of appropriate and adequate 
mental health care services.[4,6] It is quite alarming as 
close to 50% of the world’s population are residing in 
those nations, which have <1 psychiatrist per 0.1 million 
individuals.[4,6] To this, a wide disparity has been observed 
with regards to the service users/patients/persons’ country 
of residence, as the estimated number of mental health 
workers in high-income nations is 1 mental health worker 
per 2000 persons, in contrast to the estimates of <1/0.1 
million individuals in low-middle income nations such 
as Armenia, Bhutan, Bolivia, India, etc.[4]

In addition, it was revealed that the global spending on 
mental health per person is quite low and variable, with 
low and middle-income countries spending less than 
US$ 2 per capita per year, in contrast to the high-income 
nations which are spending more than US$ 50.[4,6] On 
subsequent analysis of the financial expenditure, it was 
observed that a major proportion of spent money was 
on mental health hospitals, which caters to the need 
for a very small percentage of people who actually 
need attention.[4,6] Moreover, issues pertaining to the 
poor awareness among the general population, lack of 
trained and competent health personnel and absent/
irregular supply of basic medicines to treat mental 
illnesses, especially in rural and remote settings have 
complicated the problem of delivery of mental health 
care services.[1,7]

On a positive note, some of the nations have started to 
show progress by creating policies/plans (two-third of 
the nations), and laws (50% of the nations) for mental 
health.[6] However, shortcomings like incomplete 

Nitin
Rectangle