Repeated Visual Acuity Testing in Low Vision Patients With Retinitis Pigmentosa Comparing the Modified Grating Test With the Freiburg Visual Acuity Test and ETDRS Charts

Abstract

Purpose: : Reports on repeated visual acuity (VA) testing in patients with severe visual loss are limited. Additionally VA tests below the measurable range of ETDRS charts are hardly available. So far only Schulze-Bonsel has validated a test, the Freiburg Visual Acuity Test (FrACT), where the vision range for hand motion (HM) and counting fingers (CF) is measurable in smaller scales. However this study did not include any patients with retinitis pigmentosa (RP). In artificial vision the grating test is preferred. With this in mind we developed a Modified Grating test and tested only low vision RP patients and compared the results with those of the FrACT and the ETDRS charts to verify its consistency.

Methods: : We tested 16 eyes of 8 patients, who were divided into 3 groups depending on their VA. Group 1 had a VA of HM (n= 6), group 2 CF (n=6) and group 3 better than CF (n=4). The Modified Grating test consists of a circle with black and white bars of the same width in a decreasing logarithmic order covering the range from 2.7 to 0.3 logMAR. The FrACT is a computerized test with Landoldt C in different directions and in decreasing order. ETDRS charts were used at different distances, group 1 at a distance of 0.5m, group 2 at 1m and for group 3 at 4m to serve as a control test. Each test was performed 4-5 times. The data were normally distributed. To compare the values we used the paired samples t-test.

Results: : The mean VA in group 1 as measured by the Modified Grating test was 1.3 logMAR and by FrACT 1.21 logMAR (p=0.21). In the group 2 the patients reached a mean VA of 0.7 logMAR with the Modified Grating Test and 0.6 logMAR with FrACT. The same VA was measured with ETDRS charts at 0,5m (0.68 logMAR, p=0.13). The group 3 had a mean VA of 0.1 logMAR with FrACT and 0.25 logMAR with ETDRS charts at 0.5m (p=0.55).

Conclusions: : Our preliminary data suggest that the Modified Grating test is a suitable test for the very low vision ranges of HM and CF and comparable to the FrACT.

Keywords: retina • low vision • visual acuity