Sunday, March 20, 2011

Optic Disc Drusen

Optic disc drusen is an eye condition in which small spherical mass of mucoproteins and mucopolysaccharides progressively calcify in the optic disc. These beads of mucoproteins are remnants of the axonal transport system of degenerated retinal ganglion cells. Also known as optic nerve head drusen (ONHD), it is a congenital and develomental disorder of the optic disc. Although visual acuity is not generally affected, the visual fields of these patients can be abnormal and deteriorate over time. Optic disc drusen may also be associated with vision loss of varying degree occasionally resulting in blindness. In children, optic disc drusen are usually buried and undectectable by fundoscopy except for a mild or moderate elevation of the optic disc. With age, the overlying axons become atrophied and the drusen become exposed and more visible.

Optic disc drusen are occurs in 1% of the population but this increases to 3.4% in individuals with a family history of ODD. About two thirds to three quarters of clinical cases are bilateral. A necropsy study of 737 cases showed a 2.4% incidence with 2 out of 15 (13%) bilateral, perhaps indicating the insidious nature of many cases. An autosomal dominant inheritance pattern with incomplete penetrance and associated inherited dysplasia of the optic disc and its blood supply is suspected. Males and females are affected at equal rates. Caucasians are the most susceptible ethnic group. In ODD optic nerve damage is progressive and insidious. Eventually 75% of patients will develop some peripheral field defects. These can include nasal step defects, enlarged blind spots, arcuate scotomas, sectoral field loss and altitudinal defects. Clinical symptoms correlate to visibility of the drusen.