What is a pattern dystrophy?
Pattern dystrophies are inherited in an autosomal dominant fashion and they involve the Retinal Pigment Epithelium (RPE). Pattern dystrophies represent a group of disorders that present in midlife with mild visual disturbances in one or both eyes. Since patients present later in life with this condition, they are often misdiagnosed as having Age-Related Macular Degeneration. Inherited pattern macular dystrophies are not a form of AMD, but they do share many important features with ARMD. These patients present with various patterns of yellow, orange or gray pigment deposits in the macular area.
Pattern Dystrophy Subtypes.
Based on the pattern of pigment distribution in the macula, this disease has been subdivided into five principle groups:
- Group 1: adult-onset foveomacular vitelliform dystrophy.
- Group 2: butterfly-shaped pigment dystrophy.
- Group 3: reticular dystrophy of the RPE.
- Group 4: multifocal pattern dystrophy simulating fundus flavimaculatus.
- Group 5: fundus pulverulentus.
Patients with pattern dystrophies may show different patterns between the two eyes. They may even show progression from one pattern to another over several years. Patients can have a pattern dystrophy in just one eye since it may not yet have presented in the fellow eye. The presence of different pattern dystrophies within the same family suggests a common etiologic continuum. Pattern dystrophies of the retinal pigment epithelium, an arrangement of a pattern of dots, lines, or branches, are infrequent fundus abnormalities.
What is adult onset foveomacular vitelliform dystrophy?
Patients with adult-onset foveomacular vitelliform dystrophy generally present with a solitary yellow subretinal lesion that's symmetric, round and slightly elevated. It is usually about 1/3 to 1 disc diameter in size (the size of the optic nerve that is visible in the retina). There is often a pigmented spot in the center. Initially, the yellow lesion may develop only in one eye. Most of the vitelliform lesions in this condition are small, but the larger ones can look identical to the "sunny-side-up" stage (looks like an egg sunny-side-up) of Best's vitelliform macular dystrophy. These can also look quite similar to bilateral serous detachments of the RPE. In differentiating Best's disease from these adult vitelliform lesions, it is important to remember that the vitelliform lesions in Best's develop in infancy or early childhood. Also, genetic linkage studies have identified Best's disease to a different chromosome. Attempts to identify common genetic linkage between Best's disease and other vitelliform macular dystrophies have been unsuccessful. The prognosis for maintaining good vision is favorable with this type. The elevated foveal lesions generally fade and leave an irregular oval or round area of RPE depigmentation. The lesions generally do not show the sort of disruption and layering of the yellow pigment that is seen with Best's vitelliform lesions. Choroidal neovascularization may occur, but it is rare.