Anisometropic amblyopia: spatial contrast sensitivity deficits in inferred magnocellular and parvocellular vision.

PURPOSE To measure achromatic spatial contrast sensitivity in patients with anisometropic amblyopia under conditions favoring inferred parvocellular (PC) or magnocellular (MC) pathway mediation. METHODS Fourteen anisometropic amblyopes (VA amblyopic eye 6/12 or lower; better eye greater than 6/7.5) and 10 age-matched, nonamplyopic controls (VA 6/6) participated. Foveal spatial contrast sensitivity was measured using localized, spatially narrow band targets (0.25-8.0 cpd) presented in the center of a steady pedestal (favoring MC detection) or a pulsed pedestal (favoring PC detection) that was set within a uniform surround. RESULTS Spatial contrast sensitivity functions were bandpass for the steady-pedestal and lowpass for the pulsed-pedestal. Under steady-pedestal adaptation, the amblyopes showed reduced spatial contrast sensitivity at intermediate frequencies (1-2 cpd), consistent with MC sensitivity loss. For the pulsed-pedestal condition, a generalized loss of sensitivity was observed across all spatial frequencies (0.5-4 cpd), consistent with PC sensitivity loss. The magnitudes of inferred MC and PC loss were similar. In the steady- and pulsed-pedestal paradigms, results for the better eye of greater than 75% of the amblyopes were normal or near normal at low and intermediate spatial frequencies. CONCLUSIONS Anisometropic amblyopia produces spatial contrast sensitivity losses in inferred PC- and MC-mediated vision, suggesting there may be anomalous processing of MC and PC signals in higher visual areas, including those with orientation and spatial frequency selective cells in the visual cortex. With spatially localized stimuli and a paradigm designed to distinguish between MC and PC vision under conditions that differ only in the interstimulus adaptation, the better eye of the amblyopes was normal or near normal.