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WHAT IS KERATOCONUS?
The cornea is the window of the eye. Light travels through the cornea,
past the lens to the retina, and then to the brain to form a visual
image. The normal corneal surface is smooth and aspheric (round in
the center), and flattened towards its outer edges. Light rays passing
through the cornea move in an undistorted manner to the retina and
project a clear image to the brain.
In patients with keratoconus, the cornea is cone-shaped; hence, the
name “keratoconus,” which is derived from the Greek word for cornea
(“kerato”) and cone-shaped (“conus”). In patients with keratoconus,
the cornea is not only cone-shaped, but the surface is also irregular,
resulting in a distorted image being projected to the brain.
Because the cornea is irregular and cone-shaped, glasses do not adequately
correct vision because they cannot conform to the shape of the eye.
Patients with keratoconus see best with rigid contact lenses, because
these lenses provide a clear surface in front of the cornea that allows
light rays to be projected clearly to the retina; hence, the vast
majority of patients are treated with rigid contact lenses. There
are, however, some excellent new surgical options for patients who
cannot tolerate rigid contacts. These options are discussed in the
section on treatments for keratoconus.
Many patients are initially unaware they have keratoconus. They go
to their eye doctor because of increasing spectacle blur or progressive
changes in their prescription. In many instances, even a good refraction
yields poor vision. Keratoconus is most often diagnosed by a cornea
specialist who can see typical findings when examining the patient
at the slit-lamp. In early forms of the disease, there may be no obvious
finding on slit-lamp evaluation and the diagnosis is made by computerized
videokeratography only.
Keratoconus typically starts at puberty and progresses into the mid-thirties,
at which time progression slows and often stops. Between the ages
of 12 and 35, it can arrest or advance at any time, and there is no
way to predict how fast it will advance, or if it will advance at
all. In general, young patients with advanced disease are more likely
to progress to the point where they require of surgical intervention.
Keratoconus may occur in one eye only, initially, but it most commonly
affects both eyes, with one eye being more severely affected than
the other. Both males and females are equally affected, and there
is no ethnic predilection, although in some parts of the world, such
as New Zealand and in certain parts of Finland, there is a higher
incidence due to genetic factors.
Despite millions of dollars being spent on the study of keratoconus,
no one truly knows the cause of the disease. There have been many
interesting theories but none of them have been proven conclusively,
nor have any of them been consistently reproduced by multiple research
groups. For example, one theory suggests that there is deficient collagen
cross-linking caused by free radicals, but there is no scientific
reproducible evidence to support such a theory. Others suggest that
eye-rubbing causes the progression of keratoconus. However, the evidence
for this is anecdotal, based on several case reports, but again there
is no reproducible scientific evidence to support this theory.
Our research group was the first to demonstrate that genetic factors
play a major role in the development of keratoconus (Wang Y, Rabinowitz
YS, Rotter J, Yang H. Genetic epidemiological study of keratoconus:
evidence for a major gene determination. American Journal of Medical
Genetics 93:403-409; 2000) Although our scientific-based evidence
supports a role for genetic factors, this does not mean that if you
have a child with keratoconus the child will necessarily develop the
disease, because only 13–15% of keratoconus patients have a family
history of keratoconus. It does mean, however, that genes play a role
in its development, and that in order to provide a medical cure, the
genes that contribute to the development of keratoconus have to be
identified and either replaced or suppressed. This is the only potential
hope for a permanent cure to stop progression of keratoconus and ensure
the cornea will no longer continue to thin.
For a comprehensive scientific review on keratoconus read the PDF
version of the following article: Rabinowitz Y. S. Keratoconus:
update and new advances. (Major review). Survey of Ophthalmology.
1998: 42:4:297- 319.)
CAUSES
The cause of keratoconus is still a mystery, but it is likely that
it is triggered by genetic, environmental, or cellular factors. Vigorous
eye rubbing might contribute to progression of the disease and should
be avoided, although there is no scientific evidence regarding this.
One theory suggests that deficient collagen cross-linking caused by
free radicals contributes to keratoconus, but this has not been supported
by scientific evidence.
SYMPTOMS
The first symptom of keratoconus is usually blurring of vision, which
prompts a person to go to the doctor seeking corrective lenses for
reading or driving. At this stage, the symptoms are no different than
for any other refractive problem of the eye. However, vision deteriorates
as keratoconus progresses, sometimes rapidly. Vision becomes worse
at all distances; night vision can be quite poor; vision may be worse
in one eye; sensitivity to light can develop; eye strain from the
effort to read can occur; and there may be itching. The condition
is not painful.
Another symptom is seeing multiple “ghostly” images. Instead of seeing
just one image, a person with keratoconus sees many images of the
same thing spread out in a chaotic pattern. This pattern does not
usually change from day to day, but over time it often takes different
forms. People might see streaking or flaring distortion around light
sources, or notice the images moving relative to one another in time
with their heartbeat.
If keratoconus is suspected, the eye physician will use special tests
to diagnose the condition and take a medical history, including any
family history of eye disease. An examination using an eye chart with
progressively smaller letters will be used, and the physician will
perform an examination of the eyes. The cornea will be examined to
detect irregular astigmatism that might suggest the possibility of
keratoconus. If necessary, further testing will be done. The diagnosis
will also include a determination of the degree of curvature of the
cornea.
VIDEOKERATOGRAPHY (Corneal
Topography)
This testing method creates highly-sophisticated computerized maps
are often used to confirm the diagnosis of keratoconus. Doctors at
Cedars-Sinai have developed highly sophisticated software to aid in
the diagnosis in patients clinically suspected of having the disease.
TREATMENTS
To find out about the very latest treatments for keratoconus including a Collagen Cross Linking
treatment trial go to www.keratoconus.com
RESEARCH AND GENETIC
FACTORS
The research group at Cedars-Sinai has contributed significantly to
the understanding and treatment of keratoconus; the group’s achievements
include:
| 1. |
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Developed a computer software
to early detect keratoconus
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| 2. |
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Identified the first molecular
defect in keratoconus
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The first group to publish
and demonstrate that inserting INTACS with the Intralase laser
is safer and more accurate than the mechanical technique
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| 4. |
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The first group in Los Angeles
to offer the Intralase laser for corneal transplants in patients
with keratoconus |
The research group at Cedars-Sinai was also the first group to
present scientific evidence supporting the role of genetic factors
in the development of keratoconus. These findings suggest that in
order to develop a medical cure, genes contributing to the development
of keratoconus will have to be identified and either replaced or
suppressed.
The Keratoconus Genetics Research Program at Cedars-Sinai is such
a program. Our scientists are trying to develop a medical cure for
keratoconus. The program is conducted by Yaron S. Rabinowitz, MD,
Principle Investigator, Cornea Specialist and Opthalmic Geneticist;
and Martha Bucaram Research Coordinator.
There are more ongoing clinical trials being conducted at Cedars-Sinai
for the treatment and understanding of keratoconus than anywhere
else in the world, including clinical trials related to:
| 1. |
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The early treatment
of keratoconus with INTACS and the Intralase laser
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| 2. |
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Identifying genes
in families with keratoconus
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| 3. |
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PRK(photorefractive
keratectomy) for keratoconus
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| 4. |
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Treatment of mild
to moderate keratoconus with INTACS and the Intralase laser
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| 5. |
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Treatment of keratoconus
with implantable contact lenses.
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| 6. |
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Lamellar transplants
in the treatment of keratoconus
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| 7. |
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Developing a molecular
genetic test to diagnose keratoconus
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Videokeratography
indices for detecting early keratoconus |
We are extremely optimistic that this research will ultimately
lead to improved treatments and an eventual cure for keratoconus.
Support from the public and private donor funding is needed to continue
these ongoing research efforts. If you are interested in participating
or would like to learn more about how you can become involved, please
contact Jacquie Navratil at: jnavratil@eyedefectsresearch.org
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Diagram illustrating the corneal irregularity, resulting in a distorted visual image seen in patients with keratoconus
Side view of a cornea in a patient with keratoconus demonstrating a "conical" cornea
Slit-lamp photo demonstrating paracentral thinning in a patient
with moderate to advanced keratoconus
A histopathological slide demonstrating the location of the deposition
iron constituting a Fleischer ring
Slit-lamp
photo demonstrating fine micro striate (Vogt’s Striae) at
the level of Descemet’s membrane
Stromal
scar typically seen in patients with moderate to advanced keratoconus
Munson’s
sign: cone overhanging the lower lid when looking down from the
top
Central corneal edema seen in a patient with "hydrops"
Slit-lamp
photograph demonstrating a tear in Descemet’s membrane seen after
hydrops has resolved
Classical
videokeratography pattern seen in keratoconus, demonstrating all
three phenotypic features commonly noted
Classification
scheme of normal videokeratographs using the absolute scale with
saggital topography
Topographic progression of keratoconus "suspect" to keratoconus over a 5-year period in a clinically normal fellow eye of a patient with unilateral keratoconus
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