Repeated Mobility Testing in Low Vision Patients With Retinitis Pigmentosa

Abstract

Purpose:: We created a visual function test (the Graz mobility test) and a visual acuity test (the modified grating test) to document visual improvement in artificial vision. Previous studies proved that our low vision tests are adequate to differentiate and grade the low vision of patients with retinitis pigmentosa. However it had been emphasized that in repeated testing the learning effect will negatively impact the visual results after implantation. For the purpose of monitoring a progress the tests should be reapplied in constant time intervals. The aim of this study was to investigate the constancy of the performance in repeated testing in low vision patients.

Methods:: Five low vision patients with a visual acuity from hand motion to 20/800 were enrolled in this study. The tests consisted of the Graz mobility test and a modified grating test. In the modified grating test, black and white bars of the same width were projected on a white screen in a decreasing order. The subjects were asked to specify the direction of the bars until the direction could not be recognized. A four alternative forced choice test method is used. The Graz mobility test consisted of four different, structurally similar and relatively short mazes with 11 obstacles of various sizes. The subjects passed through each course several times. Average walking speed and amount of contacts were recorded as an index of performance. The repeated tests were conducted in an interval of 1 week, 2 weeks, 1 month and half a year from the initial test.

Results:: In repeated testing the visual acuity remained the same in all patients. A learning effect could be observed in mobility testing. All patients reached a performance plateau within the first test session. Further tests revealed no significant improvements of visual function. Results after 6 months: patient 1, p=0.591; patient 2, p=0.072; patient 3, p=0.561; patient 4, p=0.116; patient 5, p=0.428 (paired samples t-test).

Conclusions:: The results indicate that both the modified grating test and the Graz mobility test show stabile performance. The tests prove to be reliable for repeated testing in low vision patients and the learning effect will not negatively impact the results of improved vision with retinal implants.

Clinical Trial:: Ethikkommission Graz

Keywords: vision and action