CD-ROM Today 1996 January/CD-ROM Today 1996 January.iso/dp/0389/03898.txt

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$Unique_ID{BRK03898}
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$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 }
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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
     [phone]

     NIH/National Eye Institute
     9000 Rockville Pike
     Bethesda, MD  20892
     [phone]

     Eye Bank Association of America
     1511 K Street NW,  Suite 830
     Washington, DC  20005-1401
     [phone]

     Eye Research Institute of Retina Foundation
     20 Staniford St.
     Boston, MA  02114
     [phone]

     Vision Foundation, Inc.
     818 Mt. Auburn Street
     Watertown, MA  02172
     [phone]
     1-800-852-3029 (Inside Massachusetts)

     National Association for the Visually Handicapped (NAVH)
     305 East 24th Street
     New York, NY  10010
     [phone]
     or
     3201 Balboa Street
     San Francisco, CA  94121
     [phone]

For Genetic Information and genetic counseling referrals:

     March of Dimes Birth Defects Foundation
     1275 Mamaroneck Avenue
     White Plains, NY  10605
     [phone]

     Alliance of Genetic Support Groups
     35 Wisconsin Circle, Suite 440
     Chevy Chase, MD  20815
     (800) 336-GENE
     [phone]

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.