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Comparison of the ETDRS logMAR, 'compact reduced logMar' and Snellen charts in routine clinical practice
L-A Lim1, N A Frost, R J Powell
1Ophthalmology Department, The West of England Eye Unit, Royal Devon and Exeter Foundation Trust, Exeter, Devon, UK. leiailim@doctors.org.uk
Aim:
To compare the performance of the ETDRS logMAR, compact reduced logMAR and Snellen charts in an ophthalmic outpatient setting.
Methods:
The reliability and reading times of the charts were compared in a stratified sample of 40 eyes of 40 ophthalmic patients with a variety of stable eye diseases. In order to simulate a clinical setting, forced-choice testing was not used.
Results:
Similar acuity results were recorded from all three charts, suggesting a lack of a systematic bias as regards chart design. A small practice effect was observed for all charts but was greatest for Snellen and least for ETDRS. The test-retest variability of the charts was similar, with the 95% tolerance limit for change being +/-0.14 logMAR for ETDRS, +/-0.16 for reduced logMAR and +/-0.18 for Snellen. The mean reading times for the subjects were 34.65 s for ETDRS, 21.17 s for reduced logMAR and 18.67 s for Snellen.
Conclusion:
The performance of the compact reduced logMAR chart was intermediate between Snellen and ETDRS. The theoretical advantages of the ETDRS design were still measurable in a clinical setting but the magnitude of the advantage in terms of test-retest reliability was fairly small and the time taken to complete the EDTRS was 1.86 times that of the Snellen chart.
