May 03, 2008
Años publicados: 1988, 1989, 2004
Retinoschisis means splitting of the eye’s retina into two layers. There are two forms of this disorder. The most common is an acquired form that affects both men and women. It usually occurs in middle age or beyond, although it can occur earlier, and it is sometimes known as senile retinoschisis. The other form is present at birth (congenital) and affects mostly boys and young men. It is known as juvenile, X-linked retinoschisis.
The disorder is characterized by a slow, progressive loss of parts of the field of vision corresponding to the areas of the retina that have become split. Either form may be associated with the development of saclike blisters (cysts) in the retina.
Retinoschisis is characterized by a reduction in visual acuity. There may also be a loss of peripheral vision. Very few people become totally blind from either form of the disorder, but some men with the juvenile form may ultimately have very poor vision.
Decreased visual acuity is directly linked to the formation of small cysts that damage the nerves in the retina. Prescribing eyeglasses cannot correct for the vision loss caused by such nerve damage. Peripheral vision is affected by the split of the retina into two layers, an inner layer of nerve cells and an outer layer of other cells.
Usually, and almost always with the juvenile form, both eyes are affected (bilateral). The juvenile form is the more serious form of retinoschisis. The acquired form may occur without symptoms (asymptomatic).
This disorder may lead to retinal detachment. The retinal split often extends back over the area near the center of the visual field (macula). If a break develops in both the front and the back layers of the retina, a true retinal detachment may occur causing loss of parts of the field of vision. A completely blind area (scotoma) with a sharp edge in the area where splitting (schisis) occurs is evident in the patient’s visual field.
The cause of acquired retinoschisis is not known. Although it often occurs in middle age or beyond, it may appear in individuals as young as 20.
Juvenile retinoschisis is transmitted genetically as an X-linked recessive trait. The mutated gene responsible is located on the short arm of the X chromosome (Xp22.2-p22.1).
Chromosomes, which are present in the nucleus of human cells, carry the genetic information for each individual. Human body cells normally have 46 chromosomes. Pairs of human chromosomes are numbered from 1 through 22 and the sex chromosomes are designated X and Y. Males have one X and one Y chromosome and females have two X chromosomes. Each chromosome has a short arm designated «p» and a long arm designated «q». Chromosomes are further sub-divided into many bands that are numbered. For example, chromosome Xp22.2-p22.1 refers to the region between bands 22.2 and 22.1 on the short arm of the X chromosome. The numbered bands specify the location of the thousands of genes that are present on each chromosome.
Genetic diseases are determined by the combination of genes for a particular trait that are on the chromosomes received from the father and the mother.
Recessive genetic disorders occur when an individual inherits the same abnormal gene for the same trait from each parent. If an individual receives one normal gene and one gene for the disease, the person will be a carrier for the disease, but usually will not show symptoms. The risk for two carrier parents to both pass the defective gene and, therefore, have an affected child is 25% with each pregnancy. The risk to have a child who is a carrier like the parents is 50% with each pregnancy. The chance for a child to receive normal genes from both parents and be genetically normal for that particular trait is 25%. The risk is the same for males and females.
All individuals carry a few abnormal genes. Parents who are close relatives (consanguineous) have a higher chance than unrelated parents to both carry the same abnormal gene, which increases the risk to have children with a recessive genetic disorder.
Dominant genetic disorders occur when only a single copy of an abnormal gene is necessary for the appearance of the disease. The abnormal gene can be inherited from either parent, or can be the result of a new mutation (gene change) in the affected individual. The risk of passing the abnormal gene from affected parent to offspring is 50% for each pregnancy regardless of the sex of the resulting child.
X-linked recessive genetic disorders are conditions caused by an abnormal gene on the X chromosome. Females have two X chromosomes but one of the X chromosomes is «turned off» and all of the genes on that chromosome are inactivated. Females who have a disease gene present on one of their X chromosomes are carriers for that disorder. Carrier females usually do not display symptoms of the disorder because it is usually the X chromosome with the abnormal gene that is «turned off». A male has one X chromosome and if he inherits an X chromosome that contains a disease gene, he will develop the disease. Males with X-linked disorders pass the disease gene to all of their daughters, who will be carriers. A male cannot pass an X-linked gene to his sons because males always pass their Y chromosome instead of their X chromosome to male offspring. Female carriers of an X-linked disorder have a 25% chance with each pregnancy to have a carrier daughter like themselves, a 25% chance to have a non-carrier daughter, a 25% chance to have a son affected with the disease, and a 25% chance to have an unaffected son.
Senile retinoschisis usually affects people in their 50s, 60s or 70s, but it has been found in persons much younger. It affects males and females in equal numbers.
Juvenile, X-linked retinoschisis affects mostly boys. However, there are very rare exceptions that occur when a girl is born to a mother who is a carrier of the disorder and an affected father. The X-linked form of the disorder is present at birth, and symptoms progress with time. The prevalence of X-linked juvenile retinoschisis is estimated at one in 5,000 to 25,000. The disorder has been detected in infants as young as three months old.
The diagnosis of retinoschisis is usually made during an examination of the back of the eye (fundus) where any splits, tears or rips may be seen. One diagnostic tool is Optical Coherence Tomography (OCT), which that uses light waves to create images of the retina.
Other tests may contribute to the diagnosis, especially an electroretinogram (ERG) that measures the electrical impulses stimulated by a light. Also, a measurement of the visual evoked response (VER) to a light stimulus is a good objective test to detect the function of the macular portion of the retina that controls central vision.
Ultrasonography or ultrasound may show abnormalities when a hemorrhage has occurred in the eye.
Senile retinoschisis does not usually require medical treatment of any kind.
In children with juvenile X-linked retinoschisis, if bleeding occurs within the eyeball, the eye is kept as still as possible in order to promote coagulation. Later, treatment with laser or cold (cryotherapy) can be applied to close off the damaged area of the retina. Surgical procedures may be a last resort of treatment. Most persons with juvenile X-linked retinoschisis usually retain functional vision.
Genetic counseling may be helpful for families of children with juvenile retinoschisis.
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FROM THE INTERNET
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