Cone and Rod Dysfunction in Fundus Albipunctatus With RDH5 Mutation: Electrophysiological Study

Abstract

Abstract: : Purpose: We have reported that some patients with fundus albipunctatus (FA) have severely reduced full–field cone ERGs. The purpose of this study was to investigate the frequency of cone dysfunction and to determine the cause for the reduced full–field cone ERGs in FA patients. We also determined whether the rod–system is affected in FA patients. Methods: Sixteen consecutive FA patients (1993 to 2003; 8 men 8 women, mean age: 25.4 yrs) with a RDH5 gene mutation were studied. The amplitudes and implicit times of the cone ERGs in the FA patients were compared to those obtained from normal subjects (n = 55). The a–waves of cone ERGs were also elicited by a bright flash and were fitted to a mathematical model of the a–wave (Birch & Hood, 1995). Rod ERG responses were elicited by dim blue flashes after 3 hours of dark–adaptation. Results: The amplitude of the b–wave of the cone ERG in the FA group varied considerably from within the normal limits to markedly decreased. Six of 16 FA patients had b–wave amplitudes that were smaller than the lowest limit of controls. The degree of cone dysfunction tended to be more severe in older patients. The analysis of the cone a–wave demonstrated that the value of Rm (maximal response amplitude) in the FA patients with reduced cone ERGs was significantly smaller than that of controls. Rod ERGs were also reduced in the FA patients who had reduced cone ERGs. Conclusions: (1) In FA patients, 38% had extensive cone dysfunction. (2) The reduced full–field cone ERGs were mainly due to the loss of cone photoreceptors. (3) The rod–system was also affected in some FA patients.

Keywords: electroretinography: clinical • retinal degenerations: hereditary