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Keratoconus

Keratoconus
Sherman Winston Reeves, M.D. M.P.H. 

Definition:

Keratoconus, which means cone-shaped cornea, is disease in which the cornea slowly thins and protrudes forward. Over time, the shape of the central cornea is changed from a sphere to one that is more cone-like, giving the disease its name. This progressive corneal warping can cause high degrees of irregular astigmatism to occur, which cannot easily be improved by glasses or soft contact lenses. Occasionally, the inside lining of the cornea, Descemet’s membrane, ruptures due to the thinning process, resulting in acute swelling of the cornea and rapid decrease in vision. When this acute swelling resolves, a scar can remain in the center of the cornea, causing permanently decreased vision.

Causes of Keratconus:

Keratocounus

The cause of keratoconus is unknown, but is likely due to many different factors. Like many diseases, a susceptibility to keratoconus is inherited from one’s parents. About 8% of keratoconus patients have a first degree family member who also has the disease. However, many individuals do not have family members who also have a history of the keratoconus. This may be due to those family members, in fact, being healthy, or due to them having very mild forms of keratoconus which do not progress or cause visual symptoms causing them to seek care and a diagnosis. Scientists are trying to determine the exact role that genetics plays in the disease process of keratoconus.
Additional, non-genetic factors may also play a role in the development of keratoconus. One such factor is frequent and aggressive eye rubbing. In a susceptible cornea, such eye rubbing may tip off or worsen the thinning and bulging process of keratoconus. Eye rubbing may just simply be a bad habit or, more commonly, may be related to other disease processes that cause the eyes to feel itchy, such as atopic dermatitis. Several other diseases, such as Down syndrome, Marfan syndrome and mitral valve prolapse, are also associated with keratoconus, though keratoconus usually occurs independently of any other disease.

Symptoms (What you may experience if you have Keratoconus):

Keratoconus is typically a disease of younger people. The first symptoms of keratoconus are usually noticed in the teenage years or 20s. At this age, a person may notice their vision getting worse. Visits to the eye doctor may reveal that their glasses prescription is constantly changing, and the astigmatism of the eye is gradually increasing. As a person ages through the 20s and 30s, the disease may worsen, requiring multiple glasses changes or the use of hard contact lenses to correct the vision. Some patients will also suffer acute corneal swelling episodes, which typically resolve over a matter of weeks. Scarring that is left behind after these episodes can permanently worsen the vision. A corneal transplant may be required in patients who cannot get visual improvement by using glasses and contact lenses alone for their keratoconus. Typically, by the time a person is 50 to 60 years of age, keratoconus slows down or stops progressing.

Examination for Keratoconus:

Tests you may have at the doctor’s office:

To determine if you have keratoconus, your eye doctor will perform an eye evaluation. Your visual acuity will be measured with an eye chart. Other general eye tests may include eye pressure measurement, pupil testing, a peripheral vision check and range-of-motion testing of the eye muscles. Your doctor will perform a slit lamp examination to examine the front part of the eye and examine the cornea for signs of keratoconus, such as corneal thinning and bulging. Your eyes may also be dilated as part of a complete eye examination to help the doctor view the vitreous and retina in the back part of the eye. The thickness of your cornea may be measured using a pachymeter, which helps your doctor assess the presence and amount of corneal thinning and/or swelling. Your doctor will likely also evaluate the shape of your cornea with a corneal topographer and or a corneal tomographer. These instruments are extremely helpful in evaluating for keratoconus and can help make the diagnosis of keratoconus even before symptoms are apparent to the patient or signs visible during the doctor’s slit lamp exam.

Treatment of Keratoconus:

Non-surgical treatment:
In the early phases of keratoconus, glasses or soft contact lenses are typically all that is required to improve the vision. In some individuals, however, the disease may advance to the point where the regular glasses and soft contact lenses are no longer effective. For these people, hard contact lenses are usually necessary to improve the vision. Most keratoconus patients can effectively be treated with hard contact lenses and enjoy good vision while the lenses are in place.

Surgical treatment:

When the vision becomes compromised significantly due to progressive warping or scarring of the cornea, surgery may be necessary to restore the vision. Several surgical approaches may be used. For corneas with moderate amounts of bulging, plastic Intacs ring segments may be placed within the cornea to help decrease the central bulging and recreate a more normal central corneal shape. Occasionally, Conductive Keratoplasty(CK) is used in conjunction with the Intacs placement to help reduce astigmatism in the cornea. Intacs and CK treatment may help improve the vision alone, or may restore enough normality to the corneal shape that contact lenses can once again be effective for improving vision. For cases of severe cornea bulging or when scarring of the cornea has also developed, a corneal transplant procedure called penetrating keratoplasty(PK) may be used to help restore the vision. During a PK, the entire cornea is removed, much like a man-hole cover, and replaced with a complete donor cornea. The donor tissue is secured in place with many sutures which are finer than a human hair. These sutures remain in place for several months, and then are slowly removed over the course of about a year. As such, the recovery period for PK is much longer than for Intacs or CK surgery for keratoconus. However, PK is sometimes the best option for visual rehabilitation, even in spite of the longer recovery.

Prognosis (How Keratoconus affects vision over the long-term):

Many people with keratoconus suffer only from mild forms of the disease and can easily be treated with glasses and/or soft contact lenses. Some patients, however, will require the permanent use of hard contact lens during their lives in order to see clearly. About 20% of keratoconus patients, however, will require a corneal transplant to help restore their vision at some point during their lives. Fortunately, corneal transplants performed in the setting of keratoconus have a very high success rate. As such, most patients who have undergone a corneal transplant for keratoconus can have useful vision restored to their eyes.

Prevention of Keratoconus:

As the exact cause of keratoconus is not well understood, there is no way to prevent the disease from occurring. Avoiding frequent and aggressive eye rubbing, however, is probably advisable, as this may hasten the development or progression of keratoconus in some people. Regular examinations by an eye doctor, however, can help identify keratoconus early and address any complications of the disease before they become visually disabling.

Thomas Eye Group

Atlanta, GA

Minnesota Eye Consultants

Minneapolis, MN