INFORMATION ABOUT LEBER CONGENITAL AMAUROSIS

Information courtesy of "The Foundation for Fighting Blindness"

Leber congenital amaurosis (LCA) is an inherited retinal degenerative disease characterized by severe loss of vision at birth. A variety of other eye-related abnormalities including roving eye movements, deep-set eyes, and sensitivity to bright light also occur with this disease. Some patients with LCA also experience central nervous system abnormalities.

Clinical description

Individuals with LCA have very reduced vision at birth. Within an infant's first few months of life, parents usually notice a lack of visual responsiveness and unusual roving eye movements, known as nystagmus. Eye examinations of infants with LCA reveal normal appearing retinas. However, electroretinography (ERG) tests, which measure visual function, detect little if any activity in the retina. A low level of retinal activity, measured by ERG, indicates very little visual function. ERG tests are key to establishing a diagnosis of LCA.

Although the causes of LCA are not well understood, researchers think the disease may either be due to an abnormal development of photoreceptor cells in the retina or to an extremely premature degeneration of these cells. The retina and its component photoreceptor cells are essential to vision as they convert light into electrical impulses and then transfer these impulses to the brain via the optic nerve.

By early adolescence, various changes in the retinas of patients with LCA become readily apparent. Blood vessels often become narrow and constricted. A variety of pigmentary (color) changes can also occur in the retinal pigment epithelium (RPE), the supportive tissue underlying the retina. Sometimes, pigmentary changes are similar to another retinal degenerative disease known as retinitis pigmentosa.

Although the appearance of the retina undergoes marked changes with age, vision usually remains fairly stable through young adult life. Long term visual prognosis remains to be defined. Visual acuity in patients with LCA is usually limited to the level of counting fingers or detecting hand motions or bright lights. Some patients are also extremely sensitive to light (photophobia). Patients with remaining vision are often extremely farsighted.

Many children with LCA habitually press on their eyes with their fists or fingers. This habitual pressing on the eyes is known clinically as oculo-digital reflex. The eyes of individuals with LCA also usually appear sunken or deep set. Keratoconus (cone shape to the front of the eye) and cataracts (clouding of the lens, the clear, glass-like structure through which light passes) have also been reported with this disease.

In some cases, LCA is associated with central nervous system complications such as developmental delay, epilepsy, and motor skill impairment. Because LCA is relatively rare, the frequency of central nervous system complications is unknown.

Inheritance

LCA is most typically passed through families by the autosomal recessive pattern of inheritance. In this type of inheritance, both parents, called carriers, have one gene for the disease paired with one normal gene. Each of their children has a 25 percent chance (or 1 chance in 4) of inheriting the two LCA genes (one from each parent) needed to cause the disorder. Carriers are unaffected because they have only one copy of the gene. At this time, it is impossible to determine who is a carrier for LCA until after the birth of an affected child.

Related diseases

Initially, LCA can be confused with early onset retinitis pigmentosa (RP), congenital and hereditary optic atrophy, cortical blindness, congenital stationary night blindness, flecked retina syndrome, and achromatopsia. Although similarly named, LCA should not be confused with Leber optic atrophy. In addition, there are syndromes seen in infancy where visual impairment at birth is a component. A thorough ophthalmologic examination including diagnostic tests measuring retinal function and an accurate documentation of family history can distinguish between these related conditions.

Treatment

Currently, there is no treatment for LCA. However, scientists have isolated three genes that contain mutations that can each cause LCA. Ongoing scientific research is directed toward understanding how these genes function in the retina and toward locating the remaining genes that cause LCA. With this information, scientists can better develop a means of prevention and treatment.

Some individuals with LCA, who have remaining vision, may benefit from the use of low-vision aids, including electronic, computer-based and optical aids. Orientation and mobility training, adaptive training skills, job placement and income assistance are available through community resources.

For more information contact:

Retina New Zealand inc.
P.O. Box 27 177
Wellington
NEW ZEALAND

Tel: [04] 389 1538
Fax: [04] 389 5254
Email: retinanz@ihug.co.nz