Measurements of eccentricity of fixation in normals and in amblyopes by evoked potentials.
A method to estimate the eccentricity of fixation, i.e. the position of the center of the fovea relative to the point of fixation, based on visually evoked potentials is described and applied to 14 normal and 17 amblyopic subjects. Eye position was simultaneously recorded. In normal subjects, the estimates of fixational eccentricity distributed unimodally with mean 12.1' and range 1-36'. The estimates from the nonamblyopic eyes of amblyopic subjects distributed bimodally with peaks near 5 and 55' and those amblyopic subjects with larger estimates were anisometropic. The results suggest that the anisometropic amblyopes have an asymmetry of retinocortical projections. When corrected for the fixational eccentricity of the nonamblyopic eye. 5 of 17 amblyopic eyes had fixational eccentricity greater than 40'. Since only 1 of these amblyopic eyes was found to fixate eccentrically by conventional clinical testing, it is suggested that eccentric fixation may be more common in amblyopia than has heretofore been appreciated.
D000550:Amblyopia / Q000503:physiopathology*; D005074:Evoked Potentials, Visual; D005403:Fixation, Ocular; D006801:Humans; D008722:Methods; D014792:Visual Acuity