Keratoconus

By Gretchyn Bailey and Judith Lee;
additional contributions and review by Gary Heiting, OD

Often appearing in the teens or early twenties, keratoconus is a progressive eye disease in which the normally round cornea thins and begins to bulge into a cone-like shape. This cone shape deflects light as it enters the eye on its way to the light-sensitive retina, causing distorted vision. Keratoconus can occur in one or both eyes.

Keratoconus Symptoms and Signs

Keratoconus can be difficult to detect, because it usually develops so slowly. However, in some cases, it may proceed rapidly. As the cornea becomes more irregular in shape, it causes progressive nearsightedness and irregular astigmatism to develop, creating additional problems with distorted and blurred vision. Glare and light sensitivity also may be noticed. Keratoconic patients often have prescription changes every time they visit their eye care practitioner. It's not unusual to have a delayed diagnosis of keratoconus, if the practitioner is not familiar with the early-stage symptoms of the disease.

What Causes Keratoconus?

New research suggests the weakening of the corneal tissue that leads to keratoconus may be due to an imbalance of enzymes within the cornea. This imbalance makes the cornea more susceptible to oxidative damage from compounds called free radicals, causing it to weaken and bulge forward.

Risk factors for oxidative damage and weakening of the cornea include a genetic predisposition, explaining why keratoconus often affects more than one member of the same family. Keratoconus is also associated with overexposure to ultraviolet rays from the sun, excessive eye rubbing, a history of poorly fit contact lenses and chronic eye irritation.

Keratoconus Treatment

In the mildest form of keratoconus, eyeglasses or soft contact lenses may help. But as the disease progresses and the cornea thins and becomes increasingly more irregular in shape, glasses or soft contacts no longer provide adequate vision correction.

Treatments for moderate and advanced keratoconus include:

Gas permeable contact lenses: If eyeglasses or soft contact lenses cannot control keratoconus, then rigid gas permeable (RGP) contact lenses are usually the preferred treatment. Their rigid lens material enables RGP lenses to vault over the cornea, replacing the cornea's irregular shape with a smooth, uniform refracting surface to improve vision.

But RGP contact lenses can be less comfortable to wear than a soft lens. Also, fitting contact lenses on a keratoconic cornea is challenging and time-consuming. You can expect frequent return visits to fine-tune the fit and the prescription, especially if the keratoconus continues to progress.

"Piggybacking" contact lenses: Because fitting a gas permeable contact lens over a cone-shaped cornea can sometimes be uncomfortable for the individual with keratoconus, some eye care practitioners advocate "piggybacking" two different types of contact lenses on the same eye. For keratoconus, this method involves placing a soft contact lens, such as one made of silicone hydrogel, over the eye and then fitting a GP lens over the soft lens. This approach increases wearer comfort because the soft lens acts like a cushioning pad under the rigid GP lens.

Normal eye vs. eye with small amount of keratoconus. The keratoconic cornea bulges slightly, for a more cone-shaped surface. (Artist's re-creation of keratometry images.)

Your eye care practitioner will monitor closely the fitting of "piggyback" contact lenses to make sure enough oxygen reaches the surface of your eye, which can be a problem when two lenses are worn on the same eye. However, most modern contacts — both GP and soft — typically have adequate oxygen permeability for a safe "piggyback" fit.

Hybrid contact lenses: Hybrid contact lenses have a relatively new design that combines a highly oxygen-permeable rigid center with a soft peripheral "skirt." Manufacturers of these lenses claim hybrid contacts provide the crisp optics of a GP lens and wearing comfort that rivals that of soft contact lenses. Hybrid lenses are also available in a wide variety of parameters to provide a fit that conforms well to the irregular shape of a keratoconic eye.

Intacs: (Addition Technology, Des Plaines, Ill.) Intacs or corneal inserts received FDA approval for treating keratoconus in August 2004. These tiny plastic inserts are placed just under the eye's surface in the periphery of the cornea and help re-shape the cornea for clearer vision. Intacs may be needed when keratoconus patients no longer can obtain functional vision with contact lenses or eyeglasses.

Several studies show that Intacs can improve the best spectacle-corrected visual acuity (BSCVA) of a keratoconic eye by an average of two lines on a standard eye chart. The implants also have the advantage of being removable and exchangeable. The surgical procedure takes only about 10 minutes. Intacs might delay but can't prevent a corneal transplant if keratoconus continues to progress.

Boston Scleral Lens Prosthetic Device (BSLPD): This cone-shaped device resembles a large contact lens and works partly by maintaining a "pool" of fluid on the eye's surface through which light rays pass and are bent to achieve proper focus. Rather than resting on the eye's clear surface or cornea, however, the lens makes contact with the "white" or sclera of the eye. The device was FDA-approved in 1994.

The BSLPD is both comfortable and able to "fill in" a highly irregular eye surface with fluid to help achieve proper focus. If other methods of keratoconus correction such as RGP contact lenses don't work, the BSLPD with its unique characteristics may be an option. To qualify for the BSLPD, you must have a severe, unusual or otherwise untreatable condition.

In cases of financial need, the non-profit Boston Foundation for Sight providing the lens will help subsidize or pay outright the $7,600 needed for lenses and fittings for both eyes. The price of a lens and fitting for one eye is $5,000. The BSLPD also has demonstrated effectiveness as a treatment for severe dry eye.

C3-R: (Boxer Wachler Vision, Los Angeles) Another new procedure for treating keratoconus, known by the brand name of C3-R (corneal collagen cross-linking with riboflavin), is a non-invasive method of strengthening corneal tissue to halt bulging of the eye's surface.

In the C3-R procedure, eye drops containing riboflavin (vitamin B2) are placed on the cornea and are then activated by ultraviolet (UV) light to strengthen links between the connective tissue (collagen) fibers within the cornea.

In the United States, FDA clinical trials for corneal collagen cross-linking began in early 2008.

Early results showing benefits of using this method have been promising. In 2008, University of Siena researchers in Italy reported positive outcomes in all 44 eyes that were followed for three years after treatment with corneal collagen cross-linking.*

Other researchers have concluded that this simple treatment method might reduce significantly the need for corneal transplants among keratoconus patients. Corneal cross-linking also is being investigated as a way to treat or prevent keratoconus-like complications following LASIK or other vision correction surgery.

Corneal transplant: Some people with keratoconus can't tolerate a rigid contact lens, or they reach the point where contact lenses or other therapies no longer provide acceptable vision. The last remedy to be considered may be a cornea transplant, also called a penetrating keratoplasty (PK or PKP). Even after a transplant, you most likely will need glasses or contact lenses for clear vision.

*American Journal of Ophthalmology, October 2008

Marilyn Haddrill also contributed to this article.

[Page updated December 2008]