Well-established visual acuity (VA) charts such as that of the Early Treatment Diabetic Retinopathy Study can quantify VA to as low as 1.6 logMAR. Below this point, clinicians must use non-quantitative measures, such as count fingers, hand movements and light perception. In an attempt to establish a more reproducible, comparable and reliable way to measure VA changes for low vision patients, researchers from the United Kingdom found that the Berkeley Rudimentary Vision Test (BRVT) and the Freiburg Acuity Test (FrACT) are both suitable options. They note that each test brought something different to the table, with the BRVT being faster to administer and the FrACT providing a numerical result in more eyes.

The team examined and compared the ability of the BRVT and the FrACT to quantify VA in low vision patients who score non-numerical VAs with standard charts. They recruited 50 adult participants with VAs ≤1.0 logMAR in both eyes and tested them with the BRVT and the FrACT. They analyzed the correlations between the results of each test and patients’ VA and daily living activities. They also investigated potential predictors of differences. 

While the BRVT was significantly faster to conduct, they found that the FrACT was able to quantify vision numerically in a greater proportion of eyes. They also discovered that the difference between the tests increased systematically with the VA reduction; further analysis showed better vision was measured on the FrACT. They add that the only significant predictor of difference between the tests was binocular VA. 

The study authors conclude that poor interest repeatability indicates that the two tests cannot be used interchangeably and note that the medium of presentation, such as a computer screen or an externally lit print medium, is likely the biggest factor in these differences and warrants further investigation.