- Keratitis is an inflammation of the cornea caused by viruses, bacteria, or occasionally from fungi. It can also occur as a result of a corneal abrasion caused by contact lenses or by an injury. Elderly persons, diabetics, those with poor tear functions, and those treated with corticosteroids may be more likely to develop keratitis after an abrasion. Keratitis is a serious infection and should be treated by an ophthalmologist. Symptoms include redness, sharp pain, tearing, impaired vision, light sensitivity, and a dulled or milky corneal surface. Simple viral keratitis is generally the least serious type. Patients are usually treated with medication on an outpatient basis. However, herpes keratitis is a very serious viral infection that can result in scarring and permanent visual impairment. Bacterial keratitis is more dangerous than viral types and often must be treated in a hospital. It may be contracted congenitally as in syphilis. The infection is treated with antibiotics and cortisone-based steroid drugs. Bacterial keratitis can permanently scar the cornea and cause vision loss. The most common forms of fungal keratitis are caused by yeasts and may require hospitalization and antifungal treatment. Scarring frequently results, despite treatment, and causes vision impairment. Another type of keratitis is exposure keratitis. This sometimes occurs when the eyelid cannot cover the eye because of bulging, as found in some thyroid conditions. Exposure keratitis can vary from mild dry spots to ulcers on the cornea.
Keratoconus is a degenerative disorder of the cornea in which the central part of the cornea thins and bulges forward into a cone shape. As the cornea thins, vision becomes distorted. As a result of further stretching, the cornea may break at the peak. The cornea will heal itself, but scar tissue will form at the break, causing vision problems. Keratoconus is a chronic, progressive disease. The exact cause is unknown, but it is thought that there is a genetic predisposition to the disorder. Most researchers agree that there probably is more than one factor involved in the cause, but there is a “trigger” that sets off a series of events in the tissues of the eye that eventually result in keratoconus. Keratoconus is most often diagnosed in children or adolescents and usually presents symptoms when they are near ten years of age. The National Keratoconus Foundation estimates that one of every two thousand people will develop the disorder. The condition may be diagnosed during a routine ophthalmologic exam which, with the use of the biomicroscope, or slit lamp, will reveal thinning of the central cornea or presence of the Fleischer ring, a narrow, greenish-brown ring in the cornea. Later stages of the disorder, in which the cornea has markedly bulged forward, can be seen without benefit of examination instruments. The disorder progresses slowly and affects both eyes. Milder forms are often corrected with spectacles or special contact lenses that cover the cornea and part of the sclera. More serious and advanced forms are corrected surgically or by a corneal transplant, called keratoplasty.
Keratometry is a measurement of the curvature of the cornea with an instrument called a keratometer. The exact keratometer measurement is used to determine the power of an intraocular lens to be implanted during cataract surgery. The greater the degree of corneal curvature, the more nearsighted is the eye and the weaker the implant needs to be. The curvature measurement and length of the eye, measured with an ultrasonic A-scan, are analyzed by a computer that calculates the strength of the implant and prescribes the precise power needed.
Keratoplasty (See Corneal Transplant.)
Keratotomy is a procedure in which incisions are made in the cornea to change its curvature over the pupil. There are two kinds of keratotomies: radial and astigmatic. Radial keratotomy, done to reduce myopia (nearsightedness), was introduced in North America in 1978. During the procedure, the surgeon makes several deep incisions in the cornea to change its curvature over the pupil. The incisions are made in a spoke-like, or radial, pattern. No cuts are made in the optical zone, which is the portion of the eye that you see through. The surgeon measures the thickness of the cornea to determine how deep to make the incisions, then, under a microscope and using a calibrated diamond blade, the surgeon will make the precise cuts. Normal pressure within the eye causes the areas around the incisions to bow, which results in a flattening of the center of the cornea. The flattened area reduces the refractive power of the cornea and allows light rays to focus on the retina, thus reducing nearsightedness. Radial keratotomy is an outpatient procedure that normally takes no more than thirty minutes to perform. Approximately 85% of people who have this type of surgery can pass a standard driver’s test that requires 20/40 vision without corrective lenses. Astigmatic keratotomy is a similar procedure that is used to reduce astigmatism. The incisions used in the procedure are made in a curved, rather than a radial pattern. Astigmatic keratotomy sometimes is used in combination with radial keratotomy to reduce myopia with astigmatism. The cornea heals slowly after the surgeries and there may be such side effects as fluctuating vision, a weakened cornea, infection, temporary pain, or difficulty in getting contact lenses to fit. Rarely, patients develop a cataract, serious infection, or experience rupture of an incision. In extreme cases, loss of vision may occur.