Optic nerve hypoplasia

Optic nerve hypoplasia is a medical condition that results in underdevelopment of the optic nerves.

Development of the optic nerve
During the second month of pregnancy, a structure called the optic stalk develops into a pair of optic nerve bundles. These bundles, which are designed to send signals from the eyes to the occipital lobe of the brain, naturally undergo pruning as the fetus develops. In some individuals, however, either this pruning process is too complete, or the nerves simply fail to develop fully. Such an occurrence causes a congenital condition called optic nerve hypoplasia (ONH).

Symptoms
Optic nerve hypoplasia can appear in one or both eyes, causing anywhere from a mild to serious visual impairment in the form of decreased visual acuity and visual fields. People with this condition are also more likely to present with photophobia and nystagmus.

Because optic nerve hypoplasia involves the underdevelopment of structures located within the brain, the condition may also be found in conjunction with a constellation of hormonal imbalances and midline brain defects known as septo-optic dysplasia.

Cause
No one is certain as to what causes optic nerve hypoplasia. The condition is usually not hereditary, but it relatively often occurs in people with albinism, which is hereditary.

There is but a weak correlation between young maternal age, or maternal diabetes, and the occurrence of this condition. It cannot be tied in with any harmful maternal activities, but there is one study that suggests children with Fetal alcohol syndrome, or prenatal alcohol exposure, often have optic nerve hypoplasia.

Prognosis
The visual prognosis in optic nerve hypoplasia is quite variable. Occasionally, optic nerve hypoplasia may be compatible with near-normal vision; in other cases, one or both eyes may be functionally, or legally blind. Although most patients with optic nerve hypoplasia lead normally productive lives, those with septo-optic dysplasia may experience non-visual problems, for example, with growth retardation.