Origin of deficits in the flicker electroretinogram of the cone system in X-linked retinoschisis as derived from response nonlinearities

The aim of this study was to identify the origin of a high-frequency attenuation in the flicker electroretinogram (ERG) of patients with X-linked retinoschisis (XLRS) through an analysis of nonlinearities in the ERG response. The ERGs of six patients with XLRS and six age-similar control subjects were recorded in response to stimuli that consisted of pairs of sinusoids that had varying temporal frequencies and that differed by either 8 or 16 Hz. Compared with the control subjects, the patients with XLRS showed a significant reduction in the amplitude of the difference frequency to high-frequency stimuli that paralleled the high-frequency attenuation of their ERG response fundamental. This result indicates that a response attenuation at an initial linear filter, most likely photoreceptoral, was a major determinant of the reduced ERG amplitude of the XLRS patients at high temporal frequencies. Additional analyses of nonlinearities in the ERG responses provided evidence of a postreceptoral component to the flicker ERG deficits of the XLRS patients, as well.