Well-established charts such as Early Treatment Diabetic Retinopathy Study are able to quantify visual acuity (VA) with a low cutoff of 1.6 logMAR. Below this point, nonquantitative measures, such as count fingers, hand movements, and light perception, are used. There is a need for more reproducible, comparable, and reliable ways to measure VA changes in this patient cohort.
The purpose of this study was to examine and compare the ability of the Berkeley Rudimentary Vision Test (BRVT) and the Freiburg Acuity Test (FrACT) to quantify VA in low-vision patients who score nonnumerical VAs in standard charts.
Fifty adult participants with VA ≤1.0 logMAR in both eyes were recruited from the Oxford Eye Hospital, Oxford, United Kingdom. Correlation between FrACT and BRVT results and the correlation between VA and daily living activities were analyzed statistically. Potential predictors of differences were investigated.
The BRVT was significantly faster to conduct (P = .002), but FrACT was able to quantify vision numerically in a greater proportion of eyes. The κ agreement between tests was 0.26. The difference increased systematically with the VA reduction (P < .0001). The Bland-Altman analysis showed a skew to measurement of lower logMAR VA indicating better vision measured on the FrACT. The only significant predictor of difference between the tests was binocular VA (coefficient, −0.445; P = .001).
Both tests are suitable for a very low-vision population. The BRVT is a faster test to administer, but FrACT provides a numerical result in more eyes. The poor intertest repeatability indicates that they cannot be used interchangeably. The BRVT generally reported poorer vision than did the FrACT. The medium of presentation, such as a computer screen or externally lit print medium, is likely to be the biggest factor in these differences and warrants further investigation.