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Keratoconus

By Gretchyn Bailey and Judith Lee;
contributions and review by Gary Heiting, OD and William Trattler, MD

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 and often begins during a person's teens or early 20s.

Keratoconus Symptoms and Signs

Keratoconus can be difficult to detect, because it usually develops slowly. However, in some cases, keratoconus 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 occur.

Often, keratoconic patients experience changes in their eyeglass prescription every time they visit their eye care practitioner.

It's not unusual to have a delayed diagnosis of keratoconus, if the practitioner is unfamiliar 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 fitted 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 and 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 or GP) contact lenses are usually the preferred treatment. Their rigid lens material enables GP lenses to vault over the cornea, replacing its irregular shape with a smooth, uniform refracting surface to improve vision.

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.)

But RGP contact lenses can be less comfortable to wear than soft contacts.

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 a person 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.

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.

Keratoconus Cure for Olympian

Bobsledder Steve Holcomb had 20/500 vision, but new procedure restored his sight. Video by NBC Nightly News

Handling GP Contact Lenses

How to apply, remove and clean your gas permeable contacts. Video by Contact Lens Manufacturers Association

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Diabetic Retinopathy

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ClearKone hybrid contact lenses. (SynergEyes Inc., Carlsbad, Calif.) These hybrid contact lenses combine a highly oxygen-permeable rigid center with a soft peripheral "skirt." The ClearKone version was designed specifically for keratoconus and vaults above the eye's cone shape for increased comfort.

The manufacturer says hybrid contacts provide the crisp optics of a GP lens and wearing comfort that rivals that of soft contact lenses.

ClearKone hybrid lenses are available in a wide variety of parameters to provide a fit that conforms well to the irregular shape of a keratoconic eye.

Scleral and semi-scleral lenses. Larger diameters found in these gas permeable (GP) lenses enable edges to rest on the eye's white sclera. Scleral lenses cover a larger portion of the sclera, whereas semi-scleral lenses cover a smaller area.

Because the center vaults over the irregularly shaped cornea, this lens doesn't apply pressure to the eye's cone-shaped surface and feels more comfortable. These types of lenses also are more stable than conventional contact lenses, which move with each blink because they cover the cornea only partially.

One example of a scleral lens is the 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.

The BSLPD also fills in a highly irregular eye surface with fluid to help achieve proper focus.

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.

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.

Corneal crosslinking. This procedure, often called CXL for short, strengthens corneal tissue to halt bulging of the eye's surface in keratoconus.

There are two versions of corneal crosslinking: epithelium-off and epithelium-on.

With epithelium-off crosslinking, the outer portion of the cornea (epithelium) is removed to allow entry of riboflavin, a type of B vitamin, into the cornea, which then is activated with UV light.

With the epithelium-on method, also called transepithelial crosslinking, the corneal surface is left intact. This epithelium-on method requires more time for the riboflavin to penetrate into the cornea, but advantages include less risk of infection, less discomfort and faster visual recovery.

In 2008, University of Siena researchers in Italy reported positive outcomes in all 44 eyes that were followed for three years after treatment with epithelium-off CXL.*

And Dr. Brian Boxer Wachler, who began performing and developing transepithelial crosslinking in 2003, has reported excellent results with keratoconus patients such as bobsledder Steve Holcomb, whose improved vision helped his team win a gold medal in the 2010 Winter Olympics. (Watch video.) Dr. Boxer Wachler, a member of the All About Vision editorial advisory board, refers to the procedure as the Holcomb C3-R, which is the first instance of a medical procedure being named for an Olympic athlete.

Several clinical trials of corneal crosslinking are in progress in the United States (where the procedure is not yet FDA-approved), and the procedure is available in other countries. The procedure may reduce significantly the need for corneal transplants among keratoconus patients. It is also being investigated as a way to treat or prevent complications following LASIK or other vision correction surgery.

Using a combination of corneal crosslinking and Intacs implants (see above) also has demonstrated promising results for treating keratoconus.

Topography-guided conductive keratoplasty. While more study is needed, early results of a small study involving topography-guided conductive keratoplasty (CK) show this procedure might help smooth irregularities in the corneal surface.

This treatment uses energy from radio waves, applied through tiny probes, to reshape the eye's surface. A topographic "map" created through imaging of the eye's surface helps create individualized treatment plans.

In October 2010, the American Journal of Ophthalmology reported that 15 of 21 keratoconic eyes treated with topography-guided CK achieved more normal corneal symmetry.

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.

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*Corneal healing after riboflavin ultraviolet-A collagen cross linking determined by confocal laser scanning microscopy in vivo: early and late modifications. American Journal of Ophthalmology, October 2008.

Marilyn Haddrill also contributed to this article.

[Page updated January 2012]