Changes in contrast sensitivity induced by defocus and their possible relations to emmetropization in the chicken

Purpose. To test whether the level of contrast adaptation (CA) relates to r efractive development in the chicken. (CA refers to a spatial frequency-sel ective increase of suprathreshold contrast sensitivity after exposure to lo w-contrast patterns). Methods. CA was determined in individual chicks by comparing their optomoto r gain in response to drifting low-contrast stripe patterns before and afte r treatment with spectacle lenses. The amount of CA was compared with the l oss of contrast predicted from defocus at the tested spatial frequency. The reversion of CA and recovery from deprivation myopia were Studied while th e retinal image features were controlled by, forcing the animals to watch s patially, filtered digital video Clips. Results. CA was induced by wearing positive and negative lenses for 1.5 hou rs, both without and with cycloplegia, but was less pronounced in the case of positive lenses when accommodation was intact. The amount of CA at a tes ted spatial frequency, was predicted from the loss of contrast calculated f rom the modulation transfer function for a defocused optical system. Watchi ng low-pass-filtered video clips induced deprivation myopia and inhibited r ecovery, from it. It also prevented the reversal of CA that was previously induced by, deprivation. Both recovery from deprivation myopia and recovery from CA occurred with sharp video clips, although less so than with normal visual exposure. Conclusions. CA changes with retinal image sharpness and occurs even when a ccommodation is intact. Because CA correlates with myopia induced by froste d occluders, negative lenses. and low-pass-filtered video clips, and its re versal correlates with recovery from myopia, it is possible that shifts in CA may represent a signal related to refractive error development.