PO Box 1097 Newcastle 2940, KwaZulu-Natal, South Africa
E-mail: pauleyes@mweb.co.za

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INTRODUCTION

Visual impairment (VI) and the delivery of accessible eye care remain major challenges in South Africa and many other countries. The traditional Snellen chart is used to measure visual acuity (VA) which is used as a useful yardstick to evaluate the level of impairment. With the advent of technology, the simple, portable Snellen chart has evolved to electronic chart projectors, embracing sophisticated digital technology systems. This article provides visual acuity (VA) tables which are useful for the classification of vision impairment.

While the traditional Snellen chart worked adequately in clinical settings, there was a need for a more accurate measure of visual acuity, especially for research purposes. In addition, there was a universal demand for visual acuity measurement, especially for patients with low vision. This necessity led to the criteria set for “New design principles for visual acuity letter charts “published in the American Journal of Optometry and Physiological Optics in 1976 by Dr Ian Bailey and his student Jan Lovie¹. The Bailey-Lovie chart has the following characteristics:

• Each line has letters of equal legibility.
• The letter and line spacing is proportional to the letter size.
• The progression of letter sizes are based on a logarithmic scale.
• Non-serifed letters are used.

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Table1. Distance visual acuity table showing equivalent VA methods. P.Ramkissoon 2024

VISUAL ACUITY
Decimal	Snellen (Metres-Metric)	Feet(USA)
0.1	6/60	20/20
0.2	6/30	20/100
0.3	6/20	20/67
0.4	6/15	20/50
0.5	6/12	20/40
0.6	6/10	20/33
0.7	6/8.6	20/29
0.8	6/7.5	20/25
0.9	6/6.7	20/22
1.0	6.6	20/20
1.2	6/3	20/10
1.5	6/1.2	20/4

 Table2. Visual acuity table showing LogMAR VA and the corresponding Snellen equivalents. P.Ramkissoon 2024

LogMAR	SNELLEN EQUIVALENT
1.0	6/60
0.9	6/48
0.8	6/38
0.7	6/30
0.6	6/24
0.5	6/19
0.4	6/15
0.3	6/12
0.2	6/9.3
0.1	6/7.5
0.0	6/6
-0.1	6/5

Table 3. Near Visual acuity table showing equivalent VA methods. P.Ramkissoon 2024

NEAR VISUAL ACUITY CONVERSION CHART
UK @ 40cm	USA @ 40cm	Distance Snellen Equivalent
N4.5	20/20	6/6
N5	20/30	6/9
N6	20/40	6/12
N10	20/60	6/18
N12	20/80	6/24
N14	20/100	6/30
N24	20/200	6/60

HOW IS VISION IMPAIRMENT CLASSIFIED?

The International Classification of Diseases (2018) classifies vision impairment into two groups, distance and near presenting vision impairment^2,3,4.

Distance vision impairment:

• Mild – presenting visual acuity worse than 6/12
• Moderate – presenting visual acuity worse than 6/18
• Severe – presenting visual acuity worse than 6/60
• Blindness – presenting visual acuity worse than 3/60

Near vision impairment:

• Presenting near visual acuity worse than N6 (6/12 distance equivalent) or N8 (6/15 distance equivalent) at 40cm with existing correction.

CONCLUSION

All visual acuity charts give eye care practitioners a useful measure of vision. However, clinically accurate charts are immensely invaluable while assessing the degree of vision impairment when evaluating eligibility for social grants, work placement and driver’s licence requirements.

REFERENCE

1. NVRI-Home to the LogMAR chart. Australian College of Optometry. Accessed 29 October 2024.
2. WHO. Fact Sheet: Blindness and vision impairment. 11 October 2018. Accessed 18 April 2019.17:21.
3. World Health Organisation. Universal eye health: a Global Action Plan 2014-2019. Geneva: World Health Organisation; 2014.
4. Billiet L, Van de Velde D, Overbury O, Van Nispen R. International classification of functioning, disability and Health core set for vision loss: A discussion paper and invitation. Vol 40.Issue 2.