Epidemiology, onset & clinical features

Epidemiology

The disease is often described as rare or very rare, through the exact prevalence remains unknown. As many of the affected individuals may be asymptomatic, the prevalence of the disorder may be underestimated. FEVR has been described in all ethnic groups.

Onset

FEVR usually occurs in full-term newborns and more frequently manifests in the first decade of life. It may however be detected at various ages, up to 20 years.

Clinical features

FEVR presents with bilateral expression that may be asymmetrical. Hallmark features include avascular peripheral retina and peripheral ischemia, retinal neovascularization, subretinal exudation, formation of an abnormal vitreoretinal interface and retinal detachment. The disease has different degrees of severity, ranging from normal vision to total blindness during the first decade of life. Highly variable expressivity may occur even within the same family.

Three clinical stages may be differentiated:

• Stage I is a mild degree of the disease in which patients are asymptomatic, but the vitreoretinal interface exhibits alterations such as white with or without pressure and cystoid degeneration as well as avascular areas in the peripheral retina. Less characteristic are vascular ingurgitation and telangectasiae, microaneurisms and arterial-venous shunts.

• Stage II is a proliferative and exudative stage that is characterized by neovascularization, fibrovascular proliferation and sub- and intra-retinal exudation. Complications (macular ectopia and papillary traction events) may occur due to fibrovascular lesions.

• In stage III, the scar lesion causes tractional, regmatogenous and exudative total or partial retina detachment and falciform folds (that may be unilateral). Other possible complications include optical atrophy, cataracts, glaucoma and strip keratopathy.

In most cases, FEVR takes a progressive course during childhood and adolescence. The progression usually stops by the age of 20 years. Ocular findings and visual acuity then usually remain stable and patients retain useful vision.