Congenital Night-Blinding Disorders With Fundus Abnormality
Fundus albipunctatus results from a mutation in RDH5 (12q13–q14). RDH5 encodes 11-cis-retinol dehydrogenase, a microsomal enzyme in the retinal pigment epithelium (RPE) that is involved in the regeneration of rhodopsin. Patients with fundus albipunctatus have very delayed rhodopsin regeneration, and although levels eventually normalize, the process may require many hours in the dark. Affected individuals are night blind from birth and usually exhibit yellow-white dots in the posterior pole extending into the midperiphery, but sparing the fovea (Fig 12-3). ERG responses commonly show a cone-isolated retina pattern, with undetectable rod-specific ERG, and a severely reduced bright-flash dark-adapted ERG (arising in dark-adapted cones) that normalizes with sufficiently extended dark adaptation. Some patients may have a normal fundus but characteristic ERG findings and molecular confirmation of the mutation; visual acuity and color vision are usually good in these patients.
The differential diagnosis of fundus albipunctatus includes retinitis punctata albescens, a disorder related to mutation in RLBP1, which encodes cellular retinaldehydebinding protein. In this condition, which is a progressive rod–cone dystrophy, the white dots may be finer than those of fundus albipunctatus, and there may be attenuation of the retinal vessels. ERG responses are usually very abnormal; although they show some recovery with extended dark adaptation, they do not normalize.
Figure 12-3 Fundus photographs and fundus autofluorescence images of a patient with fundus albipunctatus, showing multiple spots of unknown material scattered primarily throughout the deep retina.
(Used with permission from Sergouniotis PI, Sohn EH, Li Z, et al. Phenotypic variability in RDH5 retinopathy (fundus albipunctatus). Ophthalmology. 2011;118(8):1661–1670.)
Figure 12-4 Fundus photographs of eyes with the Mizuo-Nakamura phenomenon. The fundus of this patient with X-linked cone dystrophy is unremarkable in a dark-adapted state (right) but has a yellow iridescent sheen after exposure to light (left).
Patients with Oguchi disease are also night blind from birth. This condition is due to either a mutation in the gene SAG (2q37), which encodes arrestin, or in GRK1 (13q34), which encodes rhodopsin kinase. This very rare disorder is most common in Japanese patients. The fundus in eyes with Oguchi disease is normal after dark adaptation but shows a peculiar yellow iridescent sheen alteration after even brief exposure to light (the Mizuo-Nakamura phenomenon; Fig 12-4).
Cukras CA, Zein WM, Caruso RC, Sieving PA. Progressive and “stationary” inherited retinal degenerations. In: Yanoff M, Duker JS, eds. Ophthalmology. 4th ed. St. Louis: Elsevier/ Saunders; 2013:480–490.
Zeitz C, Robson AG, Audo I. Congenital stationary night blindness: an analysis and update of genotype-phenotype correlations and pathogenic mechanisms. Prog Retin Eye Res. 2015; 45:58–110.
Excerpted from BCSC 2020-2021 series: Section 10 - Glaucoma. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.