K R Alexander1, C S Barnes, G A Fishman. 1. Department of Ophthalmology and Visual Sciences, University of Illinois at Chicago 60612, USA. kennalex@uic.edu
Abstract
PURPOSE: Individuals with X-linked retinoschisis (XLRS) show a comparatively greater reduction of the ON response than the OFF response of the electroretinogram (ERG) of the cone system. At high temporal frequencies, they also show a marked attenuation of the flicker ERG that has been attributed to an abnormal cone photoreceptor response. The purpose of this study was to determine whether the high-frequency response attenuation contributes to the abnormal ERG ON response in XLRS. METHODS: Light-adapted ERGs were recorded from three patients with XLRS and from three control subjects, by using rapid-on and rapid-off sawtooth flicker to emphasize ON and OFF responses, respectively, and by using low-pass sawtooth flicker, from which the high temporal frequencies had been removed to mimic the high-frequency attenuation in XLRS. RESULTS: For the control subjects, removing the high stimulus frequencies reduced the amplitude of the b-wave component of the ON response but had little effect on the amplitude of the d-wave component of the OFF response. In the patients with XLRS, the b-wave component of the ON response was already diminished using the full sawtooth stimulus, and removing the higher stimulus frequencies had no further effect. Patients' ERG responses to the 16-Hz stimulus fundamental alone were also abnormal, in that an initial response component normally present in the ERG was absent. CONCLUSIONS: The overall pattern of findings indicates that two factors contribute to the preferential ON-response deficit in XLRS: first, a high-frequency attenuation of the cone photoreceptor response that effectively produces a low-pass stimulus for the postreceptoral pathway and that affects the ON response more than the OFF response and, second, a relatively greater attenuation of the ON- than of the OFF-bipolar cell response that is evident in the aberrant response to the sawtooth fundamental.
PURPOSE: Individuals with X-linked retinoschisis (XLRS) show a comparatively greater reduction of the ON response than the OFF response of the electroretinogram (ERG) of the cone system. At high temporal frequencies, they also show a marked attenuation of the flicker ERG that has been attributed to an abnormal cone photoreceptor response. The purpose of this study was to determine whether the high-frequency response attenuation contributes to the abnormal ERG ON response in XLRS. METHODS: Light-adapted ERGs were recorded from three patients with XLRS and from three control subjects, by using rapid-on and rapid-off sawtooth flicker to emphasize ON and OFF responses, respectively, and by using low-pass sawtooth flicker, from which the high temporal frequencies had been removed to mimic the high-frequency attenuation in XLRS. RESULTS: For the control subjects, removing the high stimulus frequencies reduced the amplitude of the b-wave component of the ON response but had little effect on the amplitude of the d-wave component of the OFF response. In the patients with XLRS, the b-wave component of the ON response was already diminished using the full sawtooth stimulus, and removing the higher stimulus frequencies had no further effect. Patients' ERG responses to the 16-Hz stimulus fundamental alone were also abnormal, in that an initial response component normally present in the ERG was absent. CONCLUSIONS: The overall pattern of findings indicates that two factors contribute to the preferential ON-response deficit in XLRS: first, a high-frequency attenuation of the cone photoreceptor response that effectively produces a low-pass stimulus for the postreceptoral pathway and that affects the ON response more than the OFF response and, second, a relatively greater attenuation of the ON- than of the OFF-bipolar cell response that is evident in the aberrant response to the sawtooth fundamental.
Authors: Agnes B Renner; Ulrich Kellner; Britta Fiebig; Elke Cropp; Michael H Foerster; Bernhard H F Weber Journal: Doc Ophthalmol Date: 2007-11-07 Impact factor: 2.379
Authors: Keith Bradshaw; Louise Allen; Dorothy Trump; Alison Hardcastle; Nicolas George; Anthony Moore Journal: Doc Ophthalmol Date: 2004-03 Impact factor: 2.379