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Keratoconus Print E-mail

Dr. Kennedy Keratoconus is a thinning of the center of the cornea (the clear surface over the colored part of the eye). This causes distortion of the shape of the cornea with resulting visual disturbance. Keratoconus is a slowly progressive condition often begining in the teens or early twenties with decreased vision and visual distortion due to severe astigmatism. Keratoconus can go undetected for long periods of time. Over 90% of patients have involvement of both eyes, though it is not unusual for there to be asymmetric changes, with one eye progressing faster than the other. In most cases the cornea is the only part of the eye that is abnormal. Family history of keratoconus is seen occasionally.

During the early stages of this disease, vision may still be correctable to 20/20 with glasses. The only clue to a keratoconus diagnosis may be from corneal measurements or a corneal topography map. A topographical map of the cornea will show the high and low spots on the cornea, much like a topographical map of the earth will show the mountains and ocean. As keratoconus progresses, vision will no longer be correctable with glasses. The cornea will thin and striations (circular lines visible with a flashlight trained on the cornea from the side. These are called Vogt's Striaes. In severe cases, a temporary painful condition called acute hydrops can occur when water rushes into the thinned area of the cornea after the posterior membrane of the cornea (Bowman's membrane) ruptures. This can lead to severe scarring and functional blindness. Hopefully before this happens the diagnosis has been made and full thickness corneal transplant, aka penetrating keratoplasty, surgery has been carried out.

The reported incidence of keratoconus varies widely from one study to the next, but the average is one out of 10,000 people develop the disease. Most people will have a mild or moderate form of the disease. Less than 10% develop the most severe form. It typically is diagnosed in the late teens or twenties. However, many are diagnosed in their mid to late thirties; this is usually a milder form of the disease. It is common for one eye to proceed faster than the other and the eyes may go for long periods of time without any change and then change dramatically over a period of months.

The cause of Keratoconus is unknown, although it is believed that it is a rare recessive gene carried by about one person out of every 200. If this is so, two of these people must produce a child to result in two of the recessive genes in one person who then develops keratoconus. Allergies, and especially asthma, tend to occur in people who will develop or have developed keratoconus. Whatever the cause, the metabolic processes are most inadequate in the center of the cornea and therefore the corneal tissue degenerates most in the center while the normal intraocular pressure pressing the cornea forward in the center producing the conical shape. Because the cornea is avascular (without direct blood supply), it depends on diffusion of oxygen from the periphery toward the center of the cornea to maintain metabolic processes. Because degeneration occurs in the center of the cornea, this leads to the suspicion that the usual lower oxygen tension in the center of the cornea somehow interacts with a genetically determined metabolic defect to produce degeneration of the centrally located corneal tissue. The periphery of the cornea is not affected by keratoconus.

The typical patient with undiagnosed keratoconus complains of deteriorating vision, usually in one eye first, both at distance and near. Near visual acuity may improve if the patient squints or holds printed material closer. Keratoconus patients often report multiple images ("ghosting" of images) due to irregular astigmatism and often relate a history of frequent refractive correction changes without much improvement in visual acuity. Patients may also report irritating symptoms such as intolerance to bright light, and a foreign body sensation in the eye. Even with appropriate contact lens correction, keratoconus patients often report fluctuating vision throughout the day and from day to day.

If the cornea is viewed from the side it is usually possible to see the conical shape. That, along with the stria mentioned above, would make it possible, at least for an eye doctor, to make the diagnosis even without special instruments. I had the disorder and once made the diagnosis in the eyes of a friend simply by looking at her cornea from the side. Like Yogi Berra once said, "It's amazing what you can see just by lookin'."

The treatment approach to keratoconus involves an orderly progression from glasses to contact lenses to corneal transplantation. In the beginning, glasses are an effective means of correcting mild keratoconus. As the cornea steepens and becomes more irregular, hard contact lenses are required to restore the spherical shape of the eye. However, contacts typically become increasingly difficult to tolerate due to the progressive irregular shape of the cornea. Corneal transplant surgery is indicated when a patient cannot wear contact lenses for an acceptable period of time or when the vision, even with contacts, is unsatisfactory. Over 90% of corneal transplants are successful with the majority of patients obtaining vision of 20/40 or better afterwards with either glasses or contact lenses. A gas permeable contact lens is the most highly effective way to manage keratoconus and 90% of all cases can be managed this way indefinitely. If the cornea becomes too scarred or painful, a corneal transplant may be necessary and, if successful, represents a permanent cure.

The information in this article is not meant to be medical advice.�Treatment for a medical condition should come at the recommendation of your personal physician.

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