Interocular ND filter suppression: Eccentricity and luminance polarity effects

Abstract

Interocular suppression as a result of wearing monocular ND filters in binocularly normal observers deepens with increasing filter strength from around 1.5 ND and higher. Incremental luminance (white) targets are suppressed more strongly over more extensive retinal areas than decremental luminance (black) targets, which are suppressed only centrally. Differences may arise from different rod-cone contributions and different ON and OFF pathway responses to dark adaptation, although discriminability differences between black and white stimuli cannot be ruled out. We suggest that with adaptation a greater shift through receptive field sizes occurs for the ON pathway, so that mismatches in size between eyes cannot be combined effectively, leading to interocular suppression. A similar mechanism can also explain suppression in binocularly anomalous participants. Clinically, increment rather than decrement luminance stimuli reveal greater levels of suppression in peripheral binocular imbalance and strabismic amblyopia. CM stimuli are more sensitive to suppression than LM stimuli and are robust to stimulus polarity; therefore, they might be most helpful in assessment of mild amblyopia and in microstrabismus.