What is Leber congenital amaurosis?
Leber congenital amaurosis (LCA) is the name given to a group of inherited diseases of the retina that lead to severe visual impairment that is present at the time of birth. LCA causes childhood blindness in three out of 100,000 people, and accounts for approximately 20 percent of children in schools for the blind.
An infant with LCA may not respond to visual stimulation and may develop unusual, wandering eye movement (nystagmus). It is common for infants with LCA to persistently press on their eyes with their fists or fingers. This behaviour is called oculo-digital sign.
Although a hallmark of LCA is extremely poor vision at birth, its symptoms vary quite dramatically from individual to individual. Some will have vision that measures as well as 20/200 on a standard reading chart (legal blindness), while others may only have the ability to detect light. In some cases, vision will remain stable, in others it will worsen over time and on rare occasions, improvement has been noted. Other variations include optical errors that range from very near-sightedness (myopia) to far-sightedness (hyperopia).
The eyes of individuals with LCA may become sunken or deep set. Keratoconus (cone shape to the front of the eye) may develop over time because of the frequent eye pressing behaviour of the oculo-digital sign. Cataracts (clouding of the lens) have also been reported as being present with this disease.
LCA is caused by defects in genes. Scientists have learned that six different genes can cause the various forms of LCA. Many genes still remain to be discovered.
Although the mechanisms that result in 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.
Infancy
Children with LCA have retinas that appear normal, so a special test called an electroretinogram (ERG) is used to detect any abnormalities in the retina's electrical activity. Individuals with LCA are found to have little or no measurable retinal activity.
Childhood and Adolescence
Changes in the retinas of individuals with LCA can be seen by early adolescence. Blood vessels in the retina often become narrow and constricted. Doctors may also detect pigmentary (colour) changes 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 changes with age, vision usually remains fairly stable through young adult life.
In rare 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.
Researchers look forward with optimism, to a future when they will be able to treat LCA. So far, the most promise appears to be with gene replacement therapy. In dogs with LCA, the RPE65 gene was replaced and the blind dog's vision was partially restored.
Click here to read about Dr. Koenekoop's FFB-C funded research study on Molecular Studies of Leber Congenital Amaurosis: A Childhood Blindness and a Model for Retinal Development Characterization of LCA.
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We would like to keep you updated with the latest news and updates, fill out the registration form to stay in touch.This information has been reviewed by:
Robert K. Koenekoop, M.D., Ph.D.
Ophthalmologist
Montreal Children's Hospital
Montreal, Quebec
This information has been provided by The Foundation Fighting Blindness - Canada and has been reviewed by its medical advisor. It is not intended to replace the advice of a qualified vision care professional. The Foundation urges everyone affected by an eye disorder to seek the best healthcare possible.