Introduction
Has a prevalence of 1 in 10,000
- Is of AD inheritance
- Onset of early childhood/adulthood and typically associated with hyperopia
- Belongs to a group of conditions known as bestrophinopathy
Pathophysiology:
- Occurs due to a mutation in the BEST1 gene, responsible for the cording of bestrophin 1
- Bestrophin 1 is a calcium channel on the RPE basolateral membrane, necessary for the maintanence of the ionic environment of RPE and subretinal space.
- Disruption leads to failed fluid transport, causing a deposit of vitelliform material in the RPE
Dead Giveaways
The main giveaway is the stages of pathophysiology, but not the vitelliform egg yolk appearance, due to the appearance in other diseases.
Stage 1: Previtelliform
Normal fundus or mild pigmentary changes
The fundus appears normal. However, a distinct ring forms around the macular
Stage 2: Vitelliform
Egg yolk lesions begins to form, with normal vision
There is a space which forms in the subretina
Stage 3: Pseudohypopyon
Looks like a hypopyon due to the buildup of the vitelliform substance in the inferior region. Vitelliform lesions is resported and remaining vitelliform gravitates downwards.
Has none to mild vision loss
The inferior drooping makes it look like an anterior chamber hypopyon.
Stage 4: Vitelliruptive
Break up the uniform vitelliform material to form a scrambled egg like appearance.
VA begins to deteriorate
The space collapses, and the FAF reveals mixed hyper/hypo-AF, which is supposed to look like a "scrambled egg"
Stage 5: End Stage
Macular atrophy, neovascularisation or subretinal fibrosis
Marked VA reduction
Fundus appears normal, with slight pigmentary changes. Macular seems more hyper-reflective than normal. On the FAF, the macula is hypo-AF. Between red arrows, the outer retina has been attenuated, which allows the increased transparency into the choroidal layer
diagnostic features
Decreased EOG may be present, however, a normal EOG can still have BEST1 disease (37.5%)
The ffERG appears normal, which can be a big differential.
Genetic testing can be a good way to identify BEST1 defect