The dependency of logMAR visual acuity measurements on chart design and scoring rule.
BACKGROUND
Visual acuity, increasingly measured using a logarithm of the minimum angle of resolution (logMAR) chart, is the "gold standard" by which the outcomes of the vast majority of clinical trials or interventions are judged. To allow comparison of results across studies, it is important that different charts provide equivalent results.


METHODS
In a first experiment, we compared corrected visual acuity measurements from four different logMAR charts (Bailey-Lovie, ETDRS, Regan, and Waterloo). In a second experiment we compared unaided visual acuity scored using a psychometric function with the more clinical by-letter scoring.


RESULTS
Experiment 1 showed significantly better visual acuity using the Regan chart compared with the other three charts, and further investigation suggested that this could be due to the font type used. Repeatability data from experiment 2 indicated that no extra repeatability was gained when using psychometric methods compared with the far simpler and quicker by-letter scoring.


CONCLUSIONS
When comparing findings between studies, the type of chart and the scoring method used may have a significant effect on the results obtained and should therefore be taken into consideration. Also, the additional time and effort demanded for determining a psychometric function for single readings of the Regan visual acuity chart is not rewarded with improved repeatability.
Hazel
Charlotte A
CA
Department of Optometry, University of Bradford, Bradford, West Yorkshire, United Kingdom. c.hazel@bradford.ac.uk
Elliott
David B
DB
D000328:Adult; D006801:Humans; D011594:Psychometrics / Q000379:methods; D015203:Reproducibility of Results; D013997:Time Factors; D014787:Vision Tests / Q000295:instrumentation* / Q000379:methods*; D014792:Visual Acuity