Best Vitelliform Macular Dystrophy

Best vitelliform macular dystrophy is an autosomal dominant disorder caused by mutations in VMD2, which encodes bestrophin [70]. Best disease usually has a childhood or teenage onset and in the early stages is typically characterised by a well-circumscribed vitelliform macular lesion, resulting from accumulation of lipofuscin at the level of the RPE. Visual acuity is usually normal until the subsequent vitelliruptive stage, resulting in disruption of overlying photoreceptors and eventual macular atrophy. The electro-physiology in Best disease is characteristic.

Full-field ERGs are normal but the electro-ocu-logram (EOG) light rise is severely reduced or undetectable, in keeping with severe generalised dysfunction affecting the RPE-photore-ceptor interface. The EOG is abnormal during the asymptomatic previtelliform stage. Pattern ERGs are typically normal until the vitellirup-tive stage, when there is visual acuity loss and, at that stage, PERG reduction. Patients younger than about 6 years are unlikely to be able to comply with EOG testing, but as the disorder is dominantly inherited it is appropriate to test the parents.

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