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Keratoconus
Definition
Keratoconus is an eye disease that affects the structure of the cornea. The cornea is the clear tissue covering the front of the eye.
The shape of the cornea slowly changes from the normal round shape to a cone shape. The eye bulges out. This causes vision problems.
Causes
The cause is unknown, but the tendency to develop keratoconus is probably present from birth. Keratoconus is thought to involve a defect in collagen, the tissue that provides strength to the cornea and gives it it's shape.
Some researchers believe that allergy and eye rubbing may play speed up damage.
There is a link between keratoconus and Down syndrome.
Symptoms
The earliest symptom is subtle blurring of vision that cannot be corrected with glasses. (Vision can most often be corrected to 20/20 with rigid, gas-permeable contact lenses.) Over time, you may have eye halos, glare, or other night vision problems.
Most people who develop keratoconus have a history of being nearsighted. The nearsightedness tends to become worse over time. As the problem gets worse, astigmatism develops.
Exams and Tests
Keratoconus is often discovered during adolescence. The most accurate test is called corneal topography, which creates a map of the curve of the cornea.
A slit-lamp examination of the cornea can diagnose the disease in the later stages.
A test called pachymetry can be used to measure the thickness of the cornea.
Treatment
Contact lenses are the main treatment for most patients with keratoconus. Wearing sunglasses outdoors after being diagnosedmay help slow or prevent the disease from becoming worse. For many years, the only surgical treatment has been corneal transplantation.
The following newer technologies may delay or prevent the need for corneal transplantation:
- High-frequency radio energy (conductive keratoplasty) to change the shape of the cornea so contact lenses work better
- Corneal implants called intracorneal ring segments to change the shape of the cornea so contact lenses work better
- An experimental treatment called corneal cross-linking causes the cornea to become hard and stops the condition from getting worse. The cornea can then be reshaped with laser vision correction.
Outlook (Prognosis)
In most cases vision can be corrected with rigid gas-permeable contact lenses.
If corneal transplantation is needed, results are usually good. The recovery period can be long, and patients often still need contact lenses.
Possible Complications
There is a risk of rejection after corneal transplantation, but the risk is much lower than with other organ transplants.
Patients with even borderline keratoconus should not have LASIK, the most common type of laser vision correction. Corneal topography is done before laser vision correction to rule out people with this condition.
In rare cases of mild keratoconus, other laser vision correction procedures may be safe to use, such as PRK. For patients treated with CK or CXL, PRK may be safe to perform and may help to further improve the vision.
When to Contact a Medical Professional
Young persons whose vision cannot be corrected to 20/20 with glasses should be evaluated by an eye doctor experienced with keratoconus. Parents with keratoconus should consider having their child or children screened for the disease starting at age 10.
Prevention
There are no preventive measures. Some specialists believe that patients with keratoconus should have their eye allergies aggressively treated and should be instructed not to rub their eyes.
References
Jain A, Paulus YM, Cockerham GC, Kenyon KR. Keratoconus and other noninflammatory corneal thinning disorders. In: Tasman W, Jaeger EA, eds. Duane's Ophthalmology. 19th ed. Philadelphia, Pa: Lippincott Williams & Wilkins; 2009:chap 16C.
Sugar J, Wadia HP. Keratoconus and other ectasias. In: Yanoff M, Duker JS, eds. Ophthalmology. 3rd ed. St. Louis, Mo: Mosby Elsevier; 2008:chap 4.18.
Dahl BJ, Spotts E, Truong JQ. Corneal collagen cross-linking: an introduction and literature review. Optometry. 2012 Jan;83(1):33-42.
Reviewed By: David Zieve, MD, MHA, Medical Director, A.D.A.M. Health Solutions, Ebix, Inc. Franklin W. Lusby, MD, Ophthalmologist, Lusby Vision Institute, La Jolla, California.
