Snellen versus logMAR visual acuity charts for evaluating driving standards in patients with neovascular macular degeneration

Abstract

Purpose:

To evaluate the use of Snellen and modified Early Treatment Diabetic Retinopathy Study (ETDRS) charts in estimating compliance with the UK Driver and Vehicle Licensing Agency visual acuity standard in patients with neovascular age-related macular degeneration.

Methods:

Patients with neovascular age-related macular degeneration in at least one eye underwent acuity test using 2m ETDRS chart, 6m Snellen chart and number plate test at 20m. The overlap zones between pass and fail in terms of ETDRS and Snellen charts were analyzed. The levels of descending acuity on the ETDRS chart that corresponded to varying percentages of patients passing or failing the number plate test were analyzed.

Results:

In total, 26 patients failed the number plate test and 24 patients passed. Fail acuities ranged from 6/36 to 6/6 on Snellen and from 49L to 79L on ETDRS chart. Pass acuities ranged from 6/12 to 6/5 on Snellen and from 67L to 85L on ETDRS chart. The overlap zone of acuities that contained patients who passed and failed was narrower with the ETDRS chart (69L–79L) compared to Snellen ( 6/6-6/12, which is equivalent to 85L-70L on ETDRS chart format).

Conclusion:

There are overlap zones of acuities in which patient’s presumptive eligibility to drive cannot be reliably estimated. An ETDRS cut-off of 77L provides a reasonable estimate of ability to pass the number plate test. These findings should provide a useful evidence base for advising patients of their compliance with the number plate test based on their logMAR acuity.