Abstract
Abstract: :
Purpose: Fast (FO) and slow oscillations (SO) of the standing potential of the eye are generated by hyper- or depolarization, respectively, of the retinal pigment epithelium's (RPE) basal membrane due to a light stimulus. The purpose of this project was to study the SO and FO in patients with Stargardt’s disease/fundus flavimaculatus (STGD), which is caused by mutations in a gene encoding a photoreceptor transporter (ABCR), and which secondarily affects RPE structure and function. Methods: 44 consecutive patients with Stargardt’s disease (28 women, 16 men, 11 to 68 years old) were studied. Mutations in the ABCR gene have been identified in a subset of these patients. The control group included 115 subjects (60 men, 55 women, 10 to 66 years old). EOGs were elicited with a Ganzfeld stimulus and recorded following ISCEV guidelines. FOs were recorded during 6 cycles of 75 sec of dark adaptation and 75 sec of light adaptation each. After pre-adaptation, SOs were recorded during 15 min of dark adaptation followed by 20 min of light adaptation. The data were analyzed using non-parametric statistical methods. Results: 1. FO. Peak-to -trough amplitude did not differ significantly between patients (132 ± 55 µV) (mean ± s.d.) and controls (148 ± 60 µV). In contrast, the mean absolute magnitude of the standing potential was considerably smaller in patients (590 ± 183 µV) than in controls (863 ± 289 µV) (P < 0.001). Therefore, the peak to trough ratio was paradoxically larger in patients (1.24 ± 0.11) than in controls (1.18 ± 0.08) (P < 0.001). The difference in phase between patients (271 ± 18 deg) and controls (276 ± 16 deg) was not significant. 2. SO. Dark trough amplitude was smaller in patients (393 ± 154 µV) than in controls (516 ± 167 µV) (P < 0.001). The reduction in light peak amplitude was even more marked in patients (787 ± 253 µV) versus controls (1255 ± 360 µV) (P < 0.001). Therefore, the Arden ratio was lower in patients (2.11 ± 0.66) than in controls (2.51 ± 0.55) (P < 0.001). The implicit time of the light peak was slightly delayed in patients (9.7± 1.5 min) versus controls (8.7± 1.2 min) (P < 0.001). Conclusions: Abnormalities in both FOs and SOs of the EOG can be present in patients with STGD; they affect the amplitude more than the time course of these oscillations. The FO changes were essentially due to a reduction of the standing potential, while the principal SO changes were secondary to a reduction in the light rise. These results reflect abnormalities in photoreceptor/RPE function in STGD. As expected, patients with macular degeneration with diffuse flecks showed more abnormal results than those with only parafoveal flecks or no flecks.
Keywords: electrophysiology: clinical • retinal degenerations: hereditary • degenerations/dystrophies