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B. Mansouri, B. Thompson, R. F. Hess; Intact Binocular Interaction in Amblyopia: A New Gateway to Treatment of Amblyopia. Invest. Ophthalmol. Vis. Sci. 2008;49(13):2594.
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© ARVO (1962-2015); The Authors (2016-present)
Our understanding of the binocular vision deficit in amblyopia has involved two different concepts; a lack of binocular connections and suppressive interocular interactions. Here we assess the extent to which binocular connections are intact in amblyopia, an issue that has significant implications for the treatment of amblyopia, as most current treatments focus exclusively on the restoration of monocular function. To address this question we used stimuli designed to minimize interocular suppressive interactions and a task that required combination of information from both eyes. We use two different tasks specifically designed to target dorsal and ventral cortical functions.
We tested 8 amblyopic and 8 normal subjects in the main experiment. We also conducted a pilot treatment experiment on 2 amblyopic subjects. We used dichopticly presented stimuli combined with signal/noise manipulations to test binocular combination. We used a dichoptic motion task to assess dorsal function and a dichoptic form task to assess ventral function. Signal and noise were presented dichoptically, signal to one eye and noise to the other. This separation of signal and noise between the two eyes allowed for direct assessment of the extent to which information was combined between the two eyes. The amount of information presented to each eye could be manipulated independently, allowing the stimuli to be biased in favor of one eye or the other. In our pilot treatment experiment, strabismic subjects were tested for 8 weeks with a motion task under stimulus conditions, defined individually for each participant, which allowed for an equal input from each eye to the binocular task.
In experiment 1, when comparable information was presented to each eye, amblyopic eyes made only a minor contribution to binocular performance. However, by reducing the information content to the fellow fixing eye, we could create conditions under which information was combined equally between the two eyes. In experiment 2, the optotype acuity for our subjects improved from 20/600 and 20/63 in the amblyopic eyes to 20/125 and 20/40, respectively. Binocular vision was also improved.
Our results demonstrate that binocular connections in amblyopia are weak but intact and able to be strengthened. Treatment of binocular function requires first adjusting the input to two eyes so that normal combination can occur and then over time, by the use of practice, gradually reducing the difference in information content between the eyes required for binocular combination. This new binocularly-based treatment of amblyopia has promise.
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