Keratoconus is an eye condition that affects the shape of the cornea, which is the clear outer covering of the eye. In this condition, the cornea thins and bulges outward, eventually resembling a cone shape. These corneal abnormalities, which worsen over time, can lead to nearsightedness (myopia), blurred vision that cannot be improved with corrective lenses (irregular astigmatism), and vision loss.

Other corneal changes typical of keratoconus that can be seen during an eye exam include iron deposits in the cornea that form a yellow-to-brownish ring, called the Fleischer ring, surrounding the colored part of the eye (iris). Affected individuals may also develop Vogt's striae, which are thin, vertical, white lines in the tissue at the back of the cornea.

Keratoconus may affect only one eye at first, but eventually the corneas of both eyes become misshapen, although they might not be affected with the same severity. As keratoconus worsens, people with this condition can develop corneal scarring, often caused by exposure of the abnormally thin cornea to prolonged contact lens use or excessive eye rubbing.

The eye changes characteristic of keratoconus typically begin in adolescence and slowly worsen until mid-adulthood at which point the shape of the cornea remains stable.

Keratoconus is the degeneration of the structure of the cornea, which is the clear tissue covering the front of the eye. In this condition, the shape of the cornea slowly changes from the normal round shape to a cone shape. Most people who develop keratoconus start out nearsighted, which tends to become worse over time. The earliest symptom is a slight blurring of vision that cannot be corrected with glasses. Over time, there may be eye halos, glare, or other night vision problems.

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 makes up most of the cornea. Some researchers believe that allergy and eye rubbing may play a role. Treatment for keratoconus depends on the severity of your condition and how quickly the condition is progressing.Mild to moderate keratoconus can be treated with eyeglasses or contact lenses.In some people the cornea becomes scarred or wearing contact lenses becomes difficult. In these cases, surgery might be necessary.

Keratoconus is usually diagnosed in teens and young adults. It causes the middle and lower parts of the cornea to get thinner over time. While a normal cornea has a rounded shape, a cornea with keratoconus can bulge outward and become a cone shape. This different cornea shape can cause vision problems.

Symptoms of keratoconus include:

• Itchy eyes
• Double vision
• Blurry vision
• Nearsightedness (when far-away objects look blurry)
• Astigmatism (when things look blurry or distorted)
• Sensitivity to light

As keratoconus gets worse, it may cause eye pain and more serious vision problems.

Most people with keratoconus can correct their vision problems by wearing glasses, soft contact lenses, or special hard contact lenses that change the shape of the cornea. Your doctor may also recommend a procedure called corneal cross-linking to strengthen your cornea. If your keratoconus causes severe corneal scarring or you have trouble wearing contact lenses, you may need a corneal transplant.

This table lists symptoms that people with this disease may have. For most diseases, symptoms will vary from person to person. People with the same disease may not have all the symptoms listed.

The exact cause of keratoconus is unknown. Both genetic and environmental factors may play a role in the development of keratoconus.

The genetic factors involve abnormalities in the structure of collagen, which result in a weak and flexible cornea. Keratoconus is more common in people with Down syndrome, Marfan syndrome, and Leber congenital amaurosis, and certain genetic conditions. In these cases, the cause depends on the specific condition.

Environmental factors may include living in sunny, hot areas of the world, while eye-rubbing is a major behavioral factor in the disease. Malfunctioning enzymes that normally help maintain the health of the cornea may play a role. All of these factors contribute to the main problem in keratoconus, which is the defective collagen structure that results in thinning and irregularity of the cornea. Keratoconus occurs more frequently in patients with atopy (asthma and eczema) or severe ocular allergies. It may also be linked to hormonal factors because it is more frequent during puberty and also may progress during pregnancy.

Corneal Topography

The measurement of curvature and shape of the anterior surface of the cornea using techniques such as keratometry, keratoscopy, photokeratoscopy, profile photography, computer-assisted image processing and videokeratography. This measurement is often applied in the fitting of contact lenses and in diagnosing corneal diseases or corneal changes including keratoconus, which occur after keratotomy and keratoplasty.

The measurement of curvature and shape of the anterior surface of the cornea using techniques such as keratometry, keratoscopy, photokeratoscopy, profile photography, computer-assisted image processing and videokeratography. This measurement is often applied in the fitting of contact lenses and in diagnosing corneal diseases or corneal changes including keratoconus, which occur after keratotomy and keratoplasty.

Treatment depends on the severity of the keratoconus symptoms and may include:

• Eyeglasses and contact lens: During early stages, vision can be corrected with eyeglasses. As the condition progresses, rigid contacts may need to be worn so that light entering the eye is refracted evenly and vision is not distorted. You should also refrain from rubbing your eyes, as this can aggravate the thin corneal tissue and make symptoms worse.
• Laser: Laser can improve corneal abrasions and contact lens tolerance.
• Implants: Keratoconus can also be treated with Intacs, which are small curved implantable corneal devices that can reshape the cornea. Intacs are FDA approved and can help flatten the steep cornea found in keratoconus.
• Collagen: Collagen cross-linking is a new treatment that uses a special laser and eyedrops to promote “cross-linking” or strengthening of the collagen fibers that make up the cornea. This treatment may flatten or stiffen the cornea, preventing further protrusion.
• Corneal transplant: When good vision is no longer possible with other treatments, a corneal transplant may be recommended. This surgery is only necessary in about 10 percent to 20 percent of patients with keratoconus. In a corneal transplant, the diseased cornea is removed and replaced with a healthy donor cornea. A transplanted cornea heals slowly. It can take up to a year or more to recover good vision after corneal transplantation. Usually contact lenses are needed afterwards.
• Deep Anterior Lamellar Keratoplasty: With this procedure, only the front and middle layers of the cornea are transplanted. The benefits of this transplant over the “full” cornea transplant is a much faster healing period and less risk of rejection.

FDA-Approved Treatments

The medication(s) listed below have been approved by the Food and Drug Administration (FDA) as orphan products for treatment of this condition.

• riboflavin ophthalmic solution & ultraviolet A(Brand name: Photrexa Viscous) - Manufactured by Avedro, Inc.
  FDA-approved indication: Treatment of progressive keratoconus.
  National Library of Medicine Drug Information Portal