Effects of prolonged dark adaptation in patients with retinitis pigmentosa of Bothnia type: an electrophysiological study

Abstract

Bothnia dystrophy (BD) is a variant of recessive retinitis punctata albescens (RPA), caused by the missense mutation R233W in cellular retinaldehyde-binding protein (CRALBP), which is localized in the retinal pigment epithelium (RPE) and Müller cells of the retina. The purpose of this study was, by examining the electrophysiological responses of the retina, to evaluate the capacity of recovery of the whole retinal area and different cell types induced by extremely prolonged dark adaptation (DA) in BD disease and to gain further understanding of the pathogenesis of BD. Six young patients underwent bilateral full-field ERGs after 24 h of DA in one eye and standard DA in the fellow eye. The results were also compared with the effect of prolonged DA (10 h), previously studied in the same patients. After extremely prolonged DA (24 h) the rod b-wave and the mixed rod-cone a-wave responses reached normal though delayed amplitudes. An increase, up to normal level, in the oscillatory response was found. There was no obvious recovery of the cone response. We conclude that in young BD patients during extremely prolonged DA there is a significant additional capacity of recovery of rod function and also significant gain of activity in the inner retinal layer. A continuous but slow regeneration of rod photopigment seems to occur at least up to 24 h. The visual process in the RPE is retarded and CRALBP acts in this process; also, the Müller cells of the retina seem to be involved. The findings also support an extremely slow synthesis of photopigments and irreversibly disturbed cone function early in BD.

Early-Onset Foveal Involvement in Retinitis Punctata Albescens With Mutations inRLBP1

“…Night blindness was the most prominent symptom and a constant finding, although rare cases have been reported with night blindness appearing in adulthood. 29 In contrast, most patients did not complain of impairment in their peripheral visual field, even at the young adult stage.…”

Congenital stationary night blindness: An analysis and update of genotype–phenotype correlations and pathogenic mechanisms

“…In the early stages the white dots may be indistinguishable from those in FA but there is typical progression characterised by scalloped areas of atrophy that eventually encroach upon the posterior pole and there may be intra-retinal pigment migration. There is some overlap with the FA ERG phenotype but ERGs are usually more severely affected and either show limited recovery following overnight DA or require even longer DA to demonstrate recovery (Burstedt et al, 2008). In the advanced stages there may be a severe rod-cone dystrophy with irreversible ERG reduction.…”

VII-2 : ELECTROPHYSIOLOGIE PEDIATRIQUE : EXEMPLES Première partie

“…Elle est due à des mutations situées dans le gène RLBP1 qui code pour une protéine de transport, importante pour les mouvements dans l'épithélium pigmentaire et les cellules de Müller (Burstedt, Sandgren, Golovleva & Wachtmeister, 2008) à l'origine de dysfonctionnement non seulement de l'épithélium pigmentaire mais aussi des photorécepteurs.…”

“…Elles peuvent atteindre une amplitude sensiblement normale après une adaptation à l'obscurité de très longue durée (24 heures) mais leurs temps de culmination restent augmentés (Granse et al, 2001). Les réponses du système photopique sont normales ou sensiblement normales, sans modification après une adaptation à l'obscurité de longue durée (Burstedt et al, 2008).…”

“…Cependant, c'est l'analyse moléculaire qui permet d'établir avec certitude le diagnostic différentiel en mettant en évidence différentes mutations dans le gène RDH5 pour le fundus albipunctatus, (Hajali et al, 2009) et dans le gène RLBP1 pour la rétinopathie ponctuée albescente (Burstedt et al, 2008). …”