Clinical trial of the use of rotating grating patterns in the treatment of amblyopia.

Abstract

Recent reports suggest that the vision in amblyopia can be significantly improved by brief weekly periods of occlusion of the good eye while the child performs concentrated visuomotor tasks against a background of rotating gratings. We have conducted a controlled trial to investigate the role played by the gratings in this procedure. One group (n=33) of amblyopic children viewed a series of rotating gratings during treatment, while the other group (n=27) performed exactly the same visuomotor tasks against a homogeneous grey background. Particular attention was placed on the choice of tests of visual acuity in order to highlight the crowding phenomenon that is a characteristic feature of the visual loss in amblyopia. The chart selected for this purpose was the Bailey-Lovie chart in which the number of letters on each line was held constant and the letter sizes and spacing were graded in equal logarithmic steps. Some improvement in vision occurred in almost all patients in either treatment group, a finding that provides support for recent claims for the effectiveness of minimal occlusion therapy. The difference between the improvement in vision of the 2 groups, averaged across all tests, was not statistically different. On only 1 of 6 acuity scores was a statistically significant difference observed in favour of the grating treatment group. However, this was observed only on patients with better than 6/60 vision where the overall improvement was itself very small. There was no detectable difference between the 2 groups either in the rate of improvement of vision or in the tendency of the vision to be maintained or even improved after cessation of treatment. Since the patients treated with gratings improved little or no more than those in the control group, we conclude that most of the visual recovery was promoted by some other aspect(s) of the procedure.