Improvement of retinal function in L-ORD after prolonged dark adaptation

Objective: To describe the changes in dark-adapted (DA) retinal electrophysiological function after prolonged dark adaptation in a cohort of patients with late-onset retinal degeneration (L-ORD). Design: Prospective case series. Participants: Nine patients with either stage 2 or 3 L-ORD. Methods: International Society for Clinical Electrophysiology of Vision standard DA electroretinograms (ERGs) were performed before and after a period of extended dark adaptation (16 hours) in a cohort of patients heterozygous for the Ser163Arg mutation in C1QTNF5. Results: Rod function was abnormal in 8 of 9 patients after standard (20 min) of dark adaptation. After extended dark adaptation, rod function normalized in 4 patients and there was a mean improvement in the DA 0.01 rod-specific ERG b-wave amplitude of 310% (p = 0.004). A significant improvement in DA 3.0 a-wave ERG amplitude localized the improvement in rod function at the level of the photoreceptor. Conclusions: This study demonstrates that a significant proportion of rod dysfunction in L-ORD can be reversed by extended dark adaptation and suggests that an abnormality of the visual cycle contributes to the pathogenesis of the disease. These findings would suggest that some retinal function could be restored, even in advanced cases of the disease if a suitable treatment is found.