Adult-onset foveomacular vitelliform dystrophy (ORPHA:99000)
A rare, genetic, macular dystrophy characterized by blurred vision, metamorphopsia and mild visual impairment secondary to a slightly elevated, yellow, egg yolk-like lesion located in the foveal or parafoveal region.
Epidemiology
The prevalence of AOFVD is unknown.
Clinical description
The clinical onset is typically between the fourth and sixth decade of life. In the early stages of AOFVD, patients are visually asymptomatic or have mild complaints of scotoma, visual blur or metamorphopsia in one or both eyes. The visual acuity usually ranges from 20/50 to 20/25. As the disease progresses, vision loss may become more severe. Choroidal neovascularization (CNV) or central retinal pigment epithelium (RPE) atrophy may result. Color vision has been reported to be slightly impaired (tritan defect).
Etiology
The mechanism underlying the physiopathology of AOFVD is still unknown but it has been postulated that there is an abnormal accumulation of lipofuscin that may be caused by the increased workload of metabolism and phagocytosis on the RPE cells in conjunction with other disease-related factors (such as age, genetic predisposition, and environmental causes). As a result, the RPE layer is separated from the photoreceptor layer by hyper-reflective material. Mutations in the genes BEST1 (11q12), PRPH2 (6p21.1) or IMPG1 (6q14.2-q15) (encoding bestrophin-1, peripherin and SPACR respectively) have been found in some individuals with AOFVD.D.
Diagnostic methods
Diagnosis of AOFVD relies on complete ophthalmologic examination, including measurement of best-corrected visual acuity (values range between 20/20-20/100), fundus biomicroscopy, fundus autofluorescence (FAF) imaging, and fluorescein angiography of optical coherent tomography when choroidal neovascularization is suspected. The minimal criteria for AOFVD diagnosis is the presence of a macular round, yellowish, more or less homogeneous lesion with fundus examination, showing hyper-autofluorescence. Electrooculogram (EOG) and electroretinogram (ERG) show normal or subnormal results (normal Arden ratio). Optical coherence tomography (OCT) reveals a vitelliform lesion located at the level of RPE or between the RPE and photoreceptors. This technique is extremely helpful in differentiating AOFVD from age-related macular degeneration (AMD; see this term).
Differential diagnosis
The differential diagnosis of AOFVD includes Best vitelliform macular dystrophy, Stargardt disease, central areolar choroidal dystrophy, central serous retinopathy (CSR), pigmented epithelial detachment (PED), basal laminar drusen, acute exudative polymorphous vitelliform maculopathy (AEPVM) (see these terms) and occult CNV secondary to AMD.
Genetic counseling
An autosomal dominant inheritance with variable expression and incomplete penetrance is suggested but AOFVD can also be sporadic without evidence of a familial inheritance pattern.
Management and treatment
There is no effective therapy for AOVFD and patients should be managed with a comprehensive eye examination, including dilation, once or twice a year to rule out any possible complications, such as CNV, full-thickness macular holes, or retinal detachments. If vision is impaired, patients should be referred for low vision testing and rehabilitation. Ranibizumab intravitreal injections may be effective in the short-term.
Prognosis
The visual prognosis of AOVFD is relatively good because the disease typically causes slow progressive vision loss, and most patients maintain decent vision in at least one eye until very late in the disease evolution. The vitelliform lesion typically disappears later in life; however, vision loss, development of a full-thickness macular hole or a retinal detachment in the late atrophic stages of the disease may be observed.

                            Last update: 
                            December 2013


                            - Expert reviewer(s): 
                             Stephanie CHAN  - Pr Ian MACDONALD