Junior Blind of America

 

Definition:
Optic Nerve Hypoplasia (ONH) refers to the underdevelopment of the optic nerve during pregnancy. The dying back of optic nerve fibers as the child develops in utero is a natural process, and ONH may be an exaggeration of that process. ONH may occur infrequently in one eye (unilateral) but more commonly in both eyes (bilateral). ONH is not progressive, is not inherited, and cannot be cured. However, depending on the degree of visual impairment, a person with this condition may benefit from the use of devices for low vision. ONH is one of the three most common causes of visual impairment in children. The effects of ONH have a broad range, from little or no visual impairment to near-total blindness.

Cause:
In most cases there is no known cause of ONH. Infrequently ONH has been associated with maternal diabetes, maternal alcohol abuse, maternal use of antiepileptic drugs, and young maternal age (20 years of age or less), but these factors account for very few of the total number of cases. All races and socioeconomic (relating to or involving economic and social factors) groups seem to be affected by ONH.

Characteristics:
Some characteristics of ONH include the following:

• ONH may occur by itself or along with neurological or hormonal abnormalities. Hormonal problems not apparent in early life may appear later
• Children with ONH demonstrate a wide spectrum of visual function ranging from normal visual acuity to no light perception. The effect on the visual field may range from generalized loss of detailed vision in both central and peripheral (side) fields (depressed visual fields) to subtle peripheral field loss
• A high percentage of children with ONH have associated involuntary rhythmic movements of the eye (nystagmus). In most cases, the nystagmus is associated with significant bilateral reduced visual acuity
• ONH is a stable condition. Visual function does not deteriorate with time. A mild improvement in visual function may occur as the result of maturation processes of the brain. In some cases, reduced nystagmus may also occur
• Mild light sensitivity (photophobia) may occur

 

Associated brain and hormonal abnormalities are common in children with nystagmus and bilateral severe vision loss, and are less common in cases where vision loss is mild or unilateral. Abnormalities include:

• Midline anomalies of the brain: septo optic dysplasia (absence of the septum pellucidum and the corpus callosum), encephaloceles, anomalies of the ventricles, anencephaly, cerebral atrophy, and rarely, tumors.
• Hormonal insufficiencies: thyroid, growth hormone, pituitary, adrenal, anti diuretic hormone (ADH)

 

ONH is diagnosed by direct examination of the eye by an ophthalmologist. No current laboratory or radiographic tests will establish the diagnosis. Many infants who are diagnosed with optic nerve atrophy are, in fact, children with ONH. Sometimes visual functioning can be predicted from the appearance of the optic discs. However, it is very difficult to predict visual acuity on this basis alone.

< Prev		Next >