Abstract: A device for detecting localized retinal damage derives focal responses of the retina from the global response of the retina to patterned stimuli in one's visual field. The stimuli comprises a series of patterns which spatially vary according to a function of a family of orthogonal functions. Each pattern also varies temporally either by being flashed before the patient or by being reversed in contrast at a fixed frequency. An electroretinogram (ERG) or magnetoretinogram (MRG) response of the patient's eye to the series of patterns is fed back into a computer generating the patterns. The responses are used by the computer to determine the coefficients of the transform of the function of the retinal response. The computer calculates the inverse transform associated with the orthogonal functions and provides the retinal response as a function of position on the retina. Contrast, intensity and temporal frequency of the patterns are chosen for a linear response of the eye.