Cataracts are abnormalities in the lens of the eye that cause a loss of transparency (opacity). They can occur either in one or in both eyes, and are quite common in the elderly. Congenital cataracts affect infants or young children and are considered to be a rare birth defect. Cataracts tend to cause cloudy vision, and, in many cases, may result in blindness when left untreated.
There are many types of cataracts:
Anterior polar cataract (including anterior pyramidal caratact) is a hereditary disorder occurring in children, and characterized by lesions with small white milky plaques in the front of the lens. Complete loss of vision rarely occurs, but cloudy vision and nearsightedness (myopia) are common.
Atopic cataract is characterized by variable loss of vision. It is an allergic disorder associated with chronic eczema and asthma. Opacity of the eye’s lens occurs, causing decreased sharpness of vision.
Complicated cataract is characterized by gradual blindness and severe nearsightedness (myopia). This disorder may be caused by a lesion inside the eye, by disease of the vascular middle coat of the eye (uvea), or other degeneration of the lens. A rosette-shaped opacity may be seen in the central part of the lens.
Congenital cataract is a vision disorder present at birth. It is characterized by a loss of transparency (opacity) of the lenses, usually in both eyes. The white opacity may be generalized or there may be a few spots that may vary in form and location. The spots may occur either at the center or at opposite ends of the eye’s lens. Impaired vision usually corresponds to these spots.
Coronary cataract is a common visual disorder occurring in adults, that usually does not impair vision. Zones of small opacities may occur, varying in color from gray to brown, yellow, red or blue. The opacities are arranged radially in the outer layers of the lens, leaving the center of the eye clear.
Diabetic cataract is characterized by varying degrees of vision impairment, occurring mainly in young persons with poorly controlled diabetes. A cloud of opacities in the eye’s lens resembles a snowflake. The lens rapidly acquires a uniform milky white color. The first stage of the disorder is reversible with treatment.
Electric cataract is caused in a person struck by lightning or an electric shock from high voltage electric current. It is characterized by variable impairment of vision. Dotted opacities in the both lens start at the edges and progress toward the center.
Heat ray cataract is caused by prolonged exposure of the eyes to high temperatures and absorption of heat by the pigment of the iris. The disorder is characterized by varied loss of sharp vision, caused by opacity of the disk in the rear center region of the lens. This area is surrounded by gradually developing, smaller opacities.
Irradiation cataract is caused by prolonged exposure to radioactivity or X-rays. It is characterized by varying loss of sharp vision which is related to the degree and location of the opacity.
Punctate cataract (cerulean cataract; blue dot cataract) is a hereditary opacity of the eye’s lens that is often associated with coronary cataract. light or bright blue dot shaped opacities are irregularly scattered throughout the lens. Vision is usually normal. This type of cataract may develop into senile cataract.
Secondary cataract (after-cataract) may follow the extraction of a cataract from the sac around the lens (capsule), when this capsule is torn or cut during surgery and lens fibers remain entrapped. Secondary cataracts cause blurred vision.
Toxic cataract is an opacity of the eye’s lens caused by toxic substances. Loss of clear vision varies with the degree and the location of the opacity. These types of cataracts usually occur in both eyes. Fine opacities may be mixed with iridescent crystals causing swelling, which may produce a dull gray opacity of the eye.
Traumatic cataract is an opacity of the lens caused by a perforating wound of the capsule around the eye’s lens. A contusion or a foreign body lodged in this capsule may also cause this type of cataract. Vision impairment varies with the severity and location of the damage. In children, the opacity may gradually dissolve without treatment. In adults, secondary glaucoma or detachment of the retina may follow appearance of the cataract.
Zonular cataract (lamellar cataract; perinuclear cataract) is the most common cataract in children. It may be inherited through dominant genes, or caused by malnutrition during pregnancy or early infancy. This type of cataract occurs in both eyes, shortly before or after birth. The opacity is sharply delineated, and usually consists of two opaque rings. Partial blindness may possibly occur.
Cataracts may have many different causes. Some are genetic and others are because of injury, other diseases, or for unknown reasons.
Anterior polar cataract is inherited through dominant genes and it is possibly X-linked.
The cause of atopic cataract is not known. The disorder is associated with allergies including chronic eczema and asthma.
Complicated cataract is caused by a lesion inside the eye, associated with disease of the middle coat of the eye, containing the iris (uvea).
Congenital cataract may be inherited through recessive genes, or caused by rubella contracted by a baby’s mother during pregnancy. The toxic effects of certain drugs taken during pregnancy may also cause this disorder.
Coronary cataract may be caused by an abnormality in fetal development. In some cases, it may be genetic, and sometimes it can be caused by maternal illness during pregnancy.
Diabetic cataracts are caused by the underlying diabetes. (For more information on this disorder, choose “insulin-dependent diabetes” as your search term in the Rare Disease Database.)
Electric cataracts are caused by exposure to excessive electric voltage.
Heat ray cataract is caused by prolonged exposure of the eyes to high temperatures as in glass-blowing or iron-puddling, when the excessive heat is absorbed by the pigment of the iris.
Irradiation cataract is caused by prolonged exposure of the eye to radiation.
Punctate cataract is possibly inherited through dominant genes. It is often associated with coronary cataract.
Secondary cataract may follow the surgical extraction of a cataract from the lens’ capsule.
Toxic cataract is caused by inhalation or swallowing of chemicals or drugs such as naphthalene dinitrophenol, triparanol, phenothiazines, ergot, or prolonged high doses of adrenal corticosteroids.
Traumatic cataract is caused by a perforating wound of the capsule around the lens, by a contusion of the eyeball which ruptures the capsule, or by a foreign object being introduced into the capsule.
Zonular cataract is either inherited through dominant genes, or possibly caused by malnutrition during late pregnancy or early infancy. It is commonly associated with rickets and defective enamel of the teeth. (For more information, choose “rickets” as your search term in the Rare Disease Database.)
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 4-5 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 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.
Surgery is used to remove some types of cataracts. The lens is removed and may be replaced with an implant. A patch is worn temporarily. Contact lenses may help improve sharpness of vision. During recent years lasers have been used increasingly to remove cataracts. Laser techniques are used to loosen either the cornea, the lens capsule, or other material when they are adhering to the lens. It is often possible to remove cataracts at outpatient clinics since the procedure may take only a few hours.
Information on current clinical trials is posted on the Internet at www.clinicaltrials.gov. All studies receiving U.S. government funding, and some supported by private industry, are posted on this government web site.
For information about clinical trials being conducted at the NIH Clinical Center in Bethesda, MD, contact the NIH Patient Recruitment Office:
Tollfree: (800) 411-1222
TTY: (866) 411-1010
For information about clinical trials sponsored by private sources, in the main, contact:
As of June, 2007 the web site listed 70 clinical trials dealing with cataracts.
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FROM THE INTERNET
Cataracts. Resource Guide. National Eye Institute. Last modified: December 2006.
Mayo Clinic Staff. Cataracts. Mayoclinic.com. May 19, 2006.
Cataracts. MedlinePlus. Medical Encyclopedia. Update Date: 8/8/2006.
Cataracts. EMedicineHealth. Last Editorial Review: 10/25/2005.
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