By Dr. Brandon Ayres, MD
Keratoconus causes progressive thinning and distortion of the cornea that affects approximately 1 in every 2000 people. It tends to affect younger people sometimes starting in the early teen years and progresses most rapidly through the fourth decade. As the dystrophy progresses the cornea takes on an irregular cone like shape and may develop scar tissue. The changes in the cornea seen in keratoconus lead to “irregular astigmatism.” Irregular astigmatism means that light is not able to focus on the retina even with the use of glasses or traditional soft contact lenses.
The primary treatment options fall into two categories: contact lenses and surgery. This article outlines both options.
Glasses and Contact Lenses
In the very early stages of keratoconus patients may notice a change in their prescription glasses or contact lenses. Often times what is seen is an increase in astigmatism. If the keratoconus progresses only minimally, all that will be needed is modification of the glasses prescription or possibly a soft contact lens that also corrects for astigmatism.
Keratoconus Contact Lenses
Once patients with keratoconus are dissatisfied with there vision with traditional glasses or soft contact lenses a special keratoconus contact lens may be necessary. Most commonly this contact lens will be either a hybrid or rigid gas permeable (RGP) contact lenses. It is important to understand that contact lenses may allow excellent vision, but do not actually treat or stop the progression of the underlying dystrophy.
A rigid gas permeable contact lens is able hold it’s spherical shape vaulting over the irregular cone shape of the irregular cornea. This gives a new smooth surface to refract light, restoring good vision. The use of an RGP is an excellent, non surgical, technique to restore vision in keatoconus, but the fitting of the lens can be quite challenging. Each patient with keratoconus has a uniquely shaped cornea and the shape may change over time. Many different designs of RGP’s are available for patients with keratoconus and patience is needed to get the right fit. Most people with keratoconus are able to be successfully fit with RGP’s, however, some have persistent foreign body sensation or difficulty with the lenses falling out of the eye.
Hybrid contact lenses work on a similar principal as RGP’s. This style of contact lens has a rigid gas permeable center that is fused to a soft contact lens “skirt” and therefore a hybrid of hard and soft contact lenses. By fusing the two styles of contact lenses the visual benefit of a RGP is combined with the comfort of a soft lens. As with the traditional RGP, these lenses must be specially fitted to ensure function, comfort, and safety.
Collagen Crosslinking (CXL)
Collagen crosslinking is a technique that is currently under FDA trial here in the United States, but widely available outside the country. Collagen crosslinking is a technique where vitamin B2 (also known as riboflavin) in liquid form is placed on the cornea. The cornea is then exposed to ultravioled light (UV-A). The combination of vitamin B2 and UV light increases the “linkages” in the corneal collagen. This has been shown in laboratory studies to “stiffen” the cornea. The goal of collagen crosslinking is to prevent progression of the keratoconus, not to reverse or cure it.
INTACS® Corneal Inserts
INTACS corneal inserts are small inserts that are placed in the cornea. These inserts help “flatten” the central cone of the cornea in patients with keratoconus. Once surgically implanted in the cornea the inserts are almost invisible and they cannot be felt. INTACS have been shown to help with improvement in corrected and uncorrected vision. INTACS can also be helpful in improving contact lens tolerance by reducing the conical shape of corneal in patients with keratoconus. Recent studies have shown continued improvement in patients having INTACS placed over the course of 1 year and there is some suggestion that they may help stabilize the cornea.
Approximately 20% of patients with keratoconus will have progression to the degree where corneal surgery is necessary. The most common procedure performed is a full thickness corneal transplant also know as a penetrating keratoplasty (PKP). In this surgery the diseased corneal is removed and replaced by a human donor cornea. Luckly, transplantation of the cornea is the most successful of all organ transplants with a low rejection rate. The vast majority of patients will achieve excellent vision after a transplant though it may take 12 to 18 months to achieve. Many patients will still need the assistance glasses or contact lenses for optimal vision.
A second surgical option for keratoconus is a deep anterior lamellar keratoplasty (DALK). This procedure is essentially the same as a corneal transplant except that the very thin innermost layer of the patient’s cornea, called the endothelium, is spared. The surgery will look and heal very similar to a corneal transplant except that there is a lower chance for transplant rejection. The surgery is technically much more challenging for the surgeon and sometime has to be converted into a full thickness transplant.
Most recently there has been an interest in using a laser to make the incisions for both corneal transplants and DALK surgical procedures. The laser-guided incisions allow for an exact match of the patient and donor corneas. The exact fit allows for a stronger wound and possibly faster healing with less residual astigmatism after the surgery.