Is the Cortical Magnification reduced for the amblyopic eye?

Abstract

Amblyopia is a disorder characterized by the reduced vision through one eye due to a disruption of normal visual development (because of strabismus, anisometropia, or deprivation). Its site is not retinal but is thought to be cortical. A number of previous investigations have suggested that either less cortex is allocated to the amblyopic eye or the cortical magnification factor (CMF) is reduced for the amblyopic eye (a selective foveal loss of cortical representation for central vision). We set out to answer the question of whether the cortical magnification in the striate cortex (V1) differed between the amblyopic and fellow sighted eyes of individual with amblyopia. We used the pRF mapping approach to estimates the parameters of an explicit model of the population of receptive fields within a voxel. With this analysis it is possible to determine the cortical magnification factor (CMF) as a function of retinal eccentricity. To reveal any V1 functional abnormalities, we compared fMRI activations across the central 6 between the fellow fixing (FFE) and amblyopic eyes (AME) of 5 severe amblyopes. Data were collected on a 3T scanner under monocular fixation with eye-movement monitoring using an Eyelink system. For both the fellow sighted and amblyopic eyes, PRF sizes increase and CMF decreases with eccentricity in V1. CMF in Amblyopes did not vary between FFE and AME activation and was similar to control subjects. We conclude that amblyopes, even if severe, do not have reduced cortex allocated to the fovea of their amblyopic eye in V1. Meeting abstract presented at VSS 2014