Factors limiting contrast sensitivity in experimentally amblyopic macaque monkeys

Contrast detection is impaired in amblyopes. To understand the contrast pro cessing deficit in amblyopia, we studied the effects of masking noise on co ntrast threshold in amblyopic macaque monkeys. Amblyopia developed as a res ult of either experimentally induced strabismus or anisometropia. We used r andom spatiotemporal broadband noise of varying contrast power to mask the detection of sinusoidal grating patches. We compared masking in the amblyop ic and non-amblyopic eyes. From the masking functions, we calculated equiva lent noise contrast (the noise power at which detection threshold was eleva ted by root 2) and signal-to-noise ratio (the ratio of threshold contrast t o noise contrast at high noise power). The relation between contrast thresh old and masking noise level was similar for amblyopic and non-amblyopic eye s. Although in most cases there was some elevation in equivalent noise for amblyopic compared to fellow eyes, signal-to-noise ratio showed greater var iation with the extent of amblyopia. These results support the idea that th e contrast detection deficit in amblyopia is a cortical deficit. (C) 1999 E lsevier Science Ltd. All rights reserved.