Atypical and “Occult” Macular Dystrophies
Atypical macular dystrophies include central areolar choroidal dystrophy for which PRPH2, GUCY2D, and 2 other genetic loci have been implicated in autosomal dominant inheritance (Fig 13-22). North Carolina macular dystrophy is an autosomal dominant, completely penetrant congenital and stationary maldevelopment of the macula. There is very large phenotypic variability with 3 grades of severity: grade 1, drusen; grade 2, confluent drusen; and grade 3, colobomatous-like excavated defects in the macula that sometimes resemble toxoplasmosis. (Fig 13-23). The visual acuity in eyes with North Carolina macular dystrophy can be surprisingly good, given the appearance of the macula. However, choroidal neovascularization and fibrosis can develop, resulting in visual acuity deterioration.
Although many of the macular dystrophies result in abnormal RPE pigmentation and/or accumulation of lipofuscin or drusenlike deposits, some forms of macular dystrophy, often referred to as occult macular dystrophy, do not have these associated findings. These patients frequently present with seemingly unexplained loss of central vision. ERG testing is uninformative in these cases, and the most striking clinical findings are disruption (either discrete or diffuse) of the central ellipsoid layer on OCT. The differential diagnosis can include solar retinopathy as well as early macular telangiectasia (which itself may be a type of polygenic macular dystrophy) and acute macular neuroretinopathy (either unilateral or bilateral). Mutations in RP1L1 and MFSD8 have been reported to give rise to this phenotype.
Figure 13-22 Color fundus photograph of central areolar choroidal dystrophy in a patient with autosomal dominant inheritance pattern.
(Courtesy of Mark W. Johnson, MD.)
Figure 13-23 Color fundus photographs show clinical variations in North Carolina macular dystrophy. A, Fundus of a 7-year-old patient with a cluster of peculiar yellowish-white atrophic lesions in the macula. B, Example of a severe, almost colobomatous, macular defect.
(Part A courtesy of Mark W. Johnson, MD; part B courtesy of Kent Small, MD.)
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.