Cone Dysfunction in Fundus Albipunctatus with RDH5 Mutations: Electrophysiological Study

Abstract

Abstract: : Purpose: We have reported that there are patients with fundus albipunctatus (FA) who have severely reduced cone–mediated ERGs (Miyake 1992; Nakamura 2000). The purpose of this study was to determine the prevalence of cone dysfunction in FA patients, and whether the reduced cone ERGs were due to incomplete regeneration of photopigments or to loss of cone outer segments. Methods:Fifteen consecutive FA patients (1993 to 2003; 7 men and 8 women; mean, 26.4 yrs) with the RDH5 mutations were studied. The amplitudes and the implicit times of cone–mediated ERGs in FA patients were compared to those of 54 controls. For patients with abnormally reduced cone–mediated ERGs, ERGs were also recorded after prolonged (>3 hour) dark–adaptation to determine whether incomplete regeneration of cone photopigment contributed to the reduced cone ERGs. To study the photoresponses from cone photoreceptors, the a–waves of cone–mediated ERGs elicited by bright flashes were also analyzed with the method of Birch & Hood (1995). Results:The amplitudes of the b–waves of cone–mediated ERGs in the FA group were widely distributed from those within the normal range to those that were severely reduced. Six of 15 FA patients had the b–wave amplitudes that were smaller than the lower limit of normal controls (cone dysfunction group). Even after prolonged dark–adaptation, the amplitude of cone–mediated ERGs in the cone dysfunction group remained very small. The analysis of the a–wave demonstrated that in the cone dysfunction group, the values of Rm (maximal response amplitude) were significantly smaller than those of controls. Conclusions: In our series, 40% of FA patients were found to be associated with significant cone dysfunction. The reduced cone ERGs amplitudes were not due to incomplete regeneration of cone photopigments under photopic conditions, but due to loss of cone outer segments.

Keywords: retinal degenerations: hereditary • electroretinography: clinical • photoreceptors: visual performance