Clinical Study
Eye advance online publication 26 June 2009; doi: 10.1038/eye.2009.147
Comparison of the ETDRS logMAR, 'compact reduced logMar' and Snellen charts in routine clinical practice
L-A Lim1, N A Frost2, R J Powell3 and P Hewson4
- 1The West of England Eye Unit, Royal Devon and Exeter Foundation Trust, Exeter, Devon, UK
- 2Ophthalmology Department, South Devon Healthcare NHS Trust, Torbay Hospital, Lawes Bridge, Torquay, Devon, UK
- 3Research Design Service South West, Royal Devon and Exeter Hospital, Exeter, UK
- 4School of Mathematics and Statistics, University of Plymouth, Drake Circus, Plymouth, UK
Correspondence: L-A Lim, Ophthalmology Department, Royal Devon and Exeter Foundation Trust, The West of England Eye Unit, Barrack Road, Exeter, Devon EX2 5DW, UK. Tel: +01392 411 611; Fax: +01392 406 022. E-mail: leiailim@doctors.org.uk
Received 19 November 2008; Revised 18 May 2009; Accepted 18 May 2009; Published online 26 June 2009.
Abstract
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.
Keywords:
logMAR, Snellen, compact reduced logMAR, test retest variability, reliability
