Usually diagnosed between 3 and 16 years of age, with a
mean age at manifestation of 6 years. The diagnosis is based on the characteristic
appearance of a discoid lesion in the macula, which usually is bilateral, but
may be asymmetric. The mass described in the macular area initially has the
appearance of the intact yolk of a fried egg and seems to be present at
birth. Progression of the disease with abnormal pigmentation then results in
a picture called scrambling the egg. Photoreceptor loss occurs in the affected area, and the
origin of the accumulated material is thought to derive from degenerated
pigment epithelial cells of the retina. Patients and carriers of the
disorder have abnormal responses in the electrooculogram.
Electroretinographic responses remain normal.