The optimal stimulus to elicit suppression in small-angle convergent strabismus

PURPOSE: To determine the optimal stimulus duration as well as the most appropriate luminance profile to elicit suppression in small-angle convergent strabismus. METHODS: In 10 subjects with small-angle convergent strabismus, using a device allowing binocular viewing and peripheral fusion, we determined what the optimal stimulus would be to elicit suppression. Three control subjects were also included in the study. Stimuli were shown randomly in the central 3° of the visual field of either eye. Stimulus durations were varied in seven steps from 50 to 1000 ms and three luminance-time profiles were used: square wave, triangle and half-sinus, thus yielding 2I different stimuli. The peak light intensity was the same for all stimuli. RESULTS: Suppression, defined as the difference in the threshold sensitivities under monocular vs. binocular viewing, was found with our test device in five of the ten subjects, and ranged between 3 and 33 dB. Suppression was deepest with triangular or half-sinusoidal stimuli of 400 ms duration. Square wave stimuli elicited the smallest amount of suppression. CONCLUSION: Stimuli with a gradual increment and decrement, like triangular or half-sinusoidal stimuli, with a duration of 400 ms are the most effective to elicit suppression.

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