A Randomized Crossover Study to Assess the Usability of Two New Vision Tests in Patients with Low Vision

Abstract

Significance: Well established charts such as ETDRS are able to quantify visual acuity (VA) with a low cut-off of 1.6 logMAR. Below this point, non-quantitative 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.Purpose: 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 non-numerical VAs in standard charts.Methods: Fifty adult participants with VA≤1.0 logMAR in both eyes were recruited from the Oxford Eye Hospital, UK. Correlation between FrACT and BRVT results, as well as the correlation between VA and daily living activities were analysed statistically. Potential predictors of differences were investigated.Results: BRVT was significantly faster to conduct (P = 0.002), but FrACT was able to quantify vision numerically in a greater proportion of eyes. The kappa agreement between tests was 0.26. The difference increased systematically with the VA reduction (P < 0.0001).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 = 0.001).Conclusions: 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 inter-test repeatability indicates they cannot be used interchangeably. The BRVT generally reported poorer vision than 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.

The Clinical Use of Vernier Acuity: Resolution of the Visual Cortex Is More Than Meets the Eye

“…The vernier acuity module of the Freiburg Acuity Test (FrACT) software 1 includes an automatic 2AFC staircase with the BestPEST adaptive algorithm on the direction (left or right) of horizontal offset between the position of two vertical lines. The FrACT has been well validated and established in the measurement of acuity in low vision patients ( Lange et al, 2009 ; Jolly et al, 2019 ). The vernier acuity module provides a valuable adjunct in the battery available.…”