BEST1 and Best vitelliform macular dystrophy: BVMD is caused by monoallelic variants in the BEST1 gene, which is located on chromosome 11q12.3 and encodes the integral membrane protein bestrophin 1, a chloride channel primarily found on the basolateral plasma membrane of the retinal pigment epithelium.2, 3, 4 The retinal degeneration can assume different anatomic configurations over time, as described by Gass5 in a 5-stage classification system: stage 1, previtelliform; stage 2, vitelliform; stage 3, pseudohypopyon; stage 4, vitelliruptive; and stage 5, atrophy or fibrosis.