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The Official Scientific Journal of Delhi Ophthalmological Society
Visual Acuity: Decoded
Pushkar Dhir1, Harsha Bhattacharjee1, Dipankar Das1, Barman Manabjyoti1, Ronel Soibam1, Diskit Angmo2, Parikshit Dhir3, Tarun Gupta3, Divakant Mishra1, Fazil Khuram1, Palak Chirania1
1Sri Sankaradeva Nethralaya, Guwahati, Assam, India; 2LVPEI Hyderabad, Telangana, India; 3Dhir Hospital, Bhiwani, Haryana, India
Corresponding Author:
Pushkar Dhir 
MBBS, DNB
Vitreo-Retina Services 
Sri Sankaradeva Nethralaya
Beltola, Guwahati - 781028, Assam, India
Email id: drdhir2014@gmail.com
Published Online: 31-JAN-2019
DOI: http://dx.doi.org/10.7869/djo.427
Abstract
In the current scenario of competition, paper writing, critical analysis and stardom, we forget to analyse the basics of the subject, one of which is a visual acuity standard. Being an ophthalmologist demands good understanding of visual acuity in all formats. This article emphasise on visual acuity conversions from logarithm to Snellen visual chart at 6 meter, 4 meter, 20 feet and  decimal forms.
Keywords : Snellen visual acuity, Visual acuity score, LogMAR
Introduction
Worldwide, ophthalmologists face this challenge of visual acuity conversion in day-to-day clinical practice. From writing a thesis to analyzing and presenting an article requires knowledge of different visual acuity formats. In this busy complicated super specialized scenario, there exists an easy way to understand what standardized 1.9 logarithm visual acuity means or 20/250 means on Snellens 6 meter or 4 meter chart. From our days of education to days of practice, we get to encounter Snellens chart most frequently and thus our mind likes to perceive all visual acuity in 6 meters form. 
Co-relation between Snellen and Log MAR is not well established and this creates a variability of representation which at times become difficult for an ophthalmologist to decipher, leading to retake of visual acuity in the format of choice. Also, it is not intuitive as poorer vision is recorded as a higher number in the other chart e.g. 6/36 Snellen is 0.80 Log MAR and 6/6 Snellen is 0.00 Log MAR. This paper gives an overview of different possible methods to decode the visual acuity.

Materials
Scientific calculator or Mobile phone calculator (iOS or android version; both have inbuilt scientific calculator).

Methodology
Descriptive log mar is to be read as Log MAR where MAR is Minimum Angle of resolution (in degree of arc). MAR value is one of the most important pivot to various other formats of conversion.

Basics
Four vision charts namely Log MAR chart, Snellens chart (20 feet), Snellen chart (6 meters) and Decimal chart are used in ophthalmic work up. Few set of basic rules are to be kept in mind before jumping into conversion.





Visual Acuity Score (VAS Scale)
Another expressive entity with all values in positive numbers is Visual acuity scale (VAS). Smaller the VAS value (minimum being 0), lesser the visual acuity. Higher the VAS value (maximum being 100), better the visual acuity.

VAS = 100- 50 LogMAR.

Discussion
The Snellen chart, which has been used since 1862, is easily recognized and is one of the hallmarks of the ophthalmologists consulting room. LogMAR chart has been introduced into clinical practice since it takes into account every notation, which is read by the patient accurately and it doesn’t have discrepancy of letters as previously noted with Love-Baileys chart. Testing children’s acuity accurately has always been a challenge and now even the best charts are those utilizing Log MAR.1

Conclusion
In view of research and rapidly growing new technology, standardization of methods and terminologies is very important. This article highlights the range of notations used by optometrists and ophthalmologists around the world for vision measurement, and gives a detailed insight on how to interpret one form from another.2

References
  1. Ferris F, Kassoff A, Bresnick GH, Bailey I. New Visual Acuity Charts for Clinical Research. Am J Ophthalmol 1982; 94:91-96.
  2. Hussain B, Saleh GM, Sivaprasad S, Hammond CJ. Changing from Snellen to LogMAR: debate or delay? Clin Exp Ophthalmol 2006; 34:6-8.
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CITE THIS ARTICLE
Pushkar Dhir, Harsha Bhattacharjee, Dipankar Das, Barman Manabjyoti, Ronel Soibam, Diskit Angmo, Parikshit Dhir, Tarun Gupta, Divakant Mishra, Fazil Khuram, Palak ChiraniaVisual Acuity: Decoded.DJO 2019;29:77-79
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Pushkar Dhir, Harsha Bhattacharjee, Dipankar Das, Barman Manabjyoti, Ronel Soibam, Diskit Angmo, Parikshit Dhir, Tarun Gupta, Divakant Mishra, Fazil Khuram, Palak ChiraniaVisual Acuity: Decoded.DJO [serial online] 2019[cited 2019 Feb 20];29:77-79. Available from: http://www.djo.org.in/articles/29/3/Visual-Acuity.html
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