Best disease

Description

This is an uncommon, hereditary and usually bilateral macular dystrophy, in which yellow material (lipofuscin)resembling egg yolk accumulates at the macula. The inheritance pattern is autosomal dominant, with highly variable penetrance and expression. The genetic defect has been mapped to the VMD2/ Bestmphin gene on chromosome 1 1. The mechanism of accumulation of lipofuscin is controversial, and may relate to a defect in the photoreceptors or retinal pigment epithelium.

Symptoms

Often asymptomatic. Patients may notice gradual reduction in visual acuity.

Signs

Signs are highly variable, even within affected families. The classical presentation occurs during the first or second decades, with the detection of a single, round lesion at the macula resembling an egg yolk. Lesions are usually present in both eyes, located at the fovea, and measure approximately one to two disc diameters across. Occasionally, unilateral, extrafoveal and multiple lesions occur. Despite the striking appearance of the lesions, visual acuity is initially normal or only slightly decreased in most cases. The condition may be accompanied by micropsia. Central relative scotomata may be detected on careful perimetry.

Later in life, degeneration of the lesion often occurs, resulting in an irregular, ‘scrambled egg’ appearance. The yellow material within the lesion may then develop a fluid level (‘pseudohypopyon’). These events are often accompanied by a substantial reduction in visual acuity and extension of scotomata. Further degenerative change may result in scarring or macular atrophy, and occasionally in secondary choroidal neovascular membrane formation.

Prevalence

Uncommon.

Significance

All family members require assessment. Affected patients are offered genetic counselling.

Differential diagnosis

Age-related macular degeneration.

See also

Choroidal neovascularization.

Management

Further investigations The electrooculogram (EOG) always shows depression, and the electroretinogram (ERG) is normal. These findings can be used to confirm the diagnosis in a patient with a vitelliform lesion, and also to diagnose the condition in members of affected families yet to develop clinical signs. Fluorescein angiography shows dark patches in the area of vitelliform change, as the lesion obscures the underlying retinal and choroidal perfusion.

Advice and review More than 75 per cent of patients with Best disease retain visual acuity better than 6/12 in at least one eye
at age 50 years. As there is no specific treatment, review at yearly intervals is appropriate. Patients may be issued with an Amsler grid, instructed on its use, and advised to report any change. Laser treatment When choroidal neovascularization is detected, laser treatment is applied at
a safe distance from the fovea.

Laser surgery When choroidal neovascularisation is detected, laser treatment is applied at a safe distance from the fovea.

Genetics All first-degree relatives require assessment.