$Unique_ID{BRK03898} $Pretitle{} $Title{Keratoconus} $Subject{Keratoconus Conical Cornea Congenital Keratoconus Keratoconus Posticus Circumscriptus Autosomal Dominant Keratoconus Autosomal Recessive Keratoconus Bullous Keratopathy Interstitial Keratitis Leber's Congenital Amaurosis Down Syndrome Ehlers-Danlos Syndrome Marfan Syndrome } $Volume{} $Log{} Copyright (C) 1988, 1989 National Organization for Rare Disorders, Inc. 578: Keratoconus ** IMPORTANT ** It is possible that the main title of the article (Keratoconus) is not the name you expected. Please check the SYNONYM listing to find the alternate names and disorder subdivisions covered by this article. Synonyms Conical Cornea Congenital Keratoconus DISORDER SUBDIVISIONS Keratoconus Posticus Circumscriptus Autosomal Dominant Keratoconus Autosomal Recessive Keratoconus Information on the following diseases can be found in the Related Disorders section of this report: Bullous Keratopathy Interstitial Keratitis Leber's Congenital Amaurosis Down Syndrome Ehlers-Danlos Syndrome Marfan Syndrome General Discussion ** REMINDER ** The information contained in the Rare Disease Database is provided for educational purposes only. It should not be used for diagnostic or treatment purposes. If you wish to obtain more information about this disorder, please contact your personal physician and/or the agencies listed in the "Resources" section of this report. Keratoconus is a slowly progressive enlargement of the curved transparent outer layer of fibrous tissue covering the eyeball (cornea). The resulting conical shape of the cornea causes blurred vision and other vision problems. Inherited forms of this disorder usually begin after puberty. Keratoconus can also occur in conjunction with a variety of other disorders. Symptoms Keratoconus is characterized by a slowly progressive conical projection of the curved transparent outer layer covering the eyeball (cornea). Symptoms begin in one eye and may later affect both eyes. Blurred or distorted vision (astigmatism) possibly caused by thinning of the outer layer of the cornea may occur. Keratoconus Posticus Circumscriptus is a form of Keratoconus which is characterized by mental retardation and lack of normal growth as well as the vision problems. Causes Keratoconus may occur alone or in some cases as a symptom of other disorders. This condition may be inherited as either an autosomal dominant or autosomal recessive trait, or it may occur for unknown reasons. Human traits including the classic genetic diseases, are the product of the interaction of two genes for that condition, one received from the father and one from the mother. In dominant disorders, a single copy of the disease gene (received from either the mother or father) will be expressed "dominating" the normal gene and resulting in appearance of the disease. The risk of transmitting the disorder from affected parent to offspring is 50% for each pregnancy regardless of the sex of the resulting child. In recessive disorders, the condition does not appear unless a person inherits the same defective gene from each parent. If one receives one normal gene and one gene for the disease, the person will be a carrier for the disease, but usually will show no symptoms. The risk of transmitting the disease to the children of a couple, both of whom are carriers for a recessive disorder, is twenty-five percent. Fifty percent of their children will be carriers, but healthy as described above. Twenty-five percent of their children will receive both normal genes, one from each parent and will be genetically normal. Keratoconus can also occur in conjunction with Leber's Congenital Amaurosis, Down Syndrome, Ehlers-Danlos Syndrome or Marfan Syndrome. (For additional information on these disorders, please choose the appropriate name as your search term in the Rare Disease Database or see the Related Disorders section of this report.) Affected Population Keratoconus affects females slightly more often than males, and tends to occur more often among adolescents than adults. One long-term study in the United States indicated a prevalence rate of 54.5 diagnosed cases of Keratoconus per 100,000 population. Involvement was limited to one eye in forty one percent of patients at the time of diagnosis, and both eyes were affected in 59 percent. Related Disorders Symptoms of the following disorders can be similar to those of Keratoconus. Comparisons may be useful for a differential diagnosis: Bullous Keratopathy is a condition caused by excessive fluid accumulation in the cornea, and is thought to be the result of deterioration of the inside layer of the cornea which comes from aging. Symptoms may increase after surgery for cataracts. Fluid-filled blisters (bullae) on the corneal surface rupture, causing pain and impaired vision. Interstitial Keratitis, also known as Parenchymatous Keratitis, is a chronic nonulcerative infiltration in the deep layers of the cornea of the eye, with inflammation in the part of the eyeball known as the uvea. Although this disorder is rare in the U.S., cases can occur in children as a late complication of congenital syphilis. One eye may be involved initially, but symptoms affect both eyes in time. In very rare cases, acquired syphilis or tuberculosis may lead to a form of Interstitial Keratitis among affected adults. Usually only one eye is affected in this form of the disorder. Light sensitivity (photophobia), pain, excessive tearing (lacrimation), and gradual loss of vision are common. Blisters begin in deep corneal layers, and eventually the entire cornea develops a ground glass appearance, obscuring the iris. New blood vessels grow and produce orange-red areas. Inflammation of the iris and choroid areas of the eyeball occur. Symptoms may subside after one or two months, but some vision impairment may remain even when the cornea clears completely. The following disorders may be present in conjunction with Keratoconus. They can be useful in identifying an underlying cause of some forms of this disorder: Leber's Congenital Amaurosis is a painless genetic optic nerve disorder. Progressive marked loss of central vision in one or both eyes is the primary symptom, which is determined by the amount of inflammation and resultant atrophy of the optic nerves. Normal optic disks and a congenital absence of light gathering bodies (rods and cones) of the retina occur initially, followed much later by swelling of the optic nerve head. There are no early changes in the optic nerves, blood vessels or retinas. Later, an absence or reduction of electrical activity of the retina is observed. This progressive disorder may also be transitional and overlapping with other similar diseases. Some cases may be complicated by Keratoconus, Retinitis Pigmentosa, Ophthalmoplegia, nerve deafness, or mental deterioration. (For more information on this disorder, choose "Leber" as your search term in the Rare Disease Database). Down Syndrome is the most common and readily identifiable genetic condition associated with mental retardation. It is caused by a chromosomal abnormality. One additional chromosome is present in each cell and this extra genetic material changes the orderly development of the body and brain. Keratoconus may occur in conjunction with Down Syndrome. (For more information on this disorder, choose "Down" as your search term in the Rare Disease Database). Ehlers-Danlos Syndrome is an inherited connective tissue disorder. It is characterized by the ability of patients to flex their bodies beyond the normal range (articular hypermobility), to abnormally stretch their skin (hyperelasticity of the skin), and widespread tissue fragility; i.e., skin, blood vessels and other tissues can rupture from even minor trauma. Keratoconus may occur in conjunction with this disorder. (For more information on this disorder, choose "Ehlers-Danlos" as your search term in the Rare Disease Database). Marfan Syndrome is an inherited condition, classified as a connective tissue disorder, that primarily affects the bones and ligaments (the skeletal system), the eyes, the cardiovascular system, and the lungs. People with Marfan Syndrome are unusually tall, have long arms and legs, and often have vision problems. Keratoconus may occur in conjunction with this disorder. (For more information on this disorder, choose "Marfan" as your search term in the Rare Disease Database). Therapies: Standard Treatment of the diminished clear vision in Keratoconus may involve the use of hard contact lenses although this is a temporary measure. Corneal transplants (penetrating keratoplasty or epikeratoplasty) are the only known method of halting the disease. In some cases, progression may be so slow that no treatment is required. Genetic counseling may be of benefit for patients with inherited forms of Keratoconus. Therapies: Investigational This disease entry is based upon medical information available through November 1988. Since NORD's resources are limited, it is not possible to keep every entry in the Rare Disease Database completely current and accurate. Please check with the agencies listed in the Resources section for the most current information about this disorder. Resources For more information on Keratoconus, please contact: National Organization for Rare Disorders (NORD) P.O. Box 8923 New Fairfield, CT 06812-1783 (203) 746-6518 NIH/National Eye Institute 9000 Rockville Pike Bethesda, MD 20892 (301) 496-5248 Eye Bank Association of America 1511 K Street NW, Suite 830 Washington, DC 20005-1401 (301) 628-4280 Eye Research Institute of Retina Foundation 20 Staniford St. Boston, MA 02114 (617) 742-3140 Vision Foundation, Inc. 818 Mt. Auburn Street Watertown, MA 02172 (617) 926-4232 1-800-852-3029 (Inside Massachusetts) National Association for the Visually Handicapped (NAVH) 305 East 24th Street New York, NY 10010 (212) 889-3141 or 3201 Balboa Street San Francisco, CA 94121 (414) 221-3201 For Genetic Information and genetic counseling referrals: March of Dimes Birth Defects Foundation 1275 Mamaroneck Avenue White Plains, NY 10605 (914) 428-7100 Alliance of Genetic Support Groups 35 Wisconsin Circle, Suite 440 Chevy Chase, MD 20815 (800) 336-GENE (301) 652-5553 References A 48-YEAR CLINICAL AND EPIDEMIOLOGIC STUDY OF KERATOCONUS: R.H. Kennedy, et al.; Am J Ophthalmol (March 15, 1986, issue 101(3)). Pp. 267-273. CONTACT LENS FITTING RELATION AND VISUAL ACUITY IN KERATOCONUS: K Zadnik, et al.; Am J Optom Physiol Opt (September 1987, issue 64(9)). Pp. 698-702. LONG-TERM COMPARISON OF EPIKERATOPLASTY AND PENETRATING KERATOPLASTY FOR KERATOCONUS: R.F. Steinert, et al.; Arch Ophthalmol (April 1988, issue 106(4)). Pp. 493-496. ELECTROSURGICAL KERATOPLASTY. CLINICOPATHOLOGIC CORRELATION: P.J. McDonnell, et al.; Arch Ophthalmol (February 1988, issue 106(2)). Pp. 235- 238. CORNEAL REGRAFTS: F. Bigar, et al.; Dev Ophthalmol (1987, issue 14). Pp. 117-120. MENDELIAN INHERITANCE IN MAN, 7th ed.: Victor A. McKusick; Johns Hopkins University Press, 1986. Pp. 441, 1073-1074.