Keratoconus (KEHR-a-toh-kohn-nus) is a disorder that results in the thinning of the cornea (the clear front part of the eye), causing it to bulge into a "cone" shape. The condition generally affects both eyes (bilateral), but one eye tends to be more advanced (asymmetric) than the other. In the beginning stages of keratoconus, patients may be able to achieve good vision with spectacles or soft contact lenses. As the condition progresses, and corneal surface irregularities increases, spectacles and soft lenses may no longer be able to provide acceptable vision. As a result, custom fitted gas permeable contact lenses may be necessary to restore optimal vision.
General facts on keratoconus
- Estimated occurrence is 1 out of every 2000 persons in the general population
- The disease may be diagnosed during late adolescence or early twenties
- There is no significant gender, ethnic or social pattern
- The exact cause of keratoconus is unknown
- Symptoms include blurry and/or distorted vision
- Some patients complain of itchy eyes or have associated eye rubbing tendencies
- The continued thinning of the cornea progresses slowly and may reach a plateau
Keratoconus treatmentFor 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 gas permeable (GP) contact lenses are usually the preferred treatment. The rigid lens material enables GP lenses to vault over the cornea, replacing the cornea's irregular shape with a smooth, uniform refracting surface to improve vision.
Scleral Gas Permeable contact lenses: Because fitting a gas permeable contact lens over a cone is sometimes difficult and not the most comfortable for the patient a NEW DEVELOPMENT in contact lens treatment has been developed. These lenses are more like the size of a soft contact lens with large improvements in the comfort over previous lenses. These lenses now cover up a significant amount of the distortions associated with keratoconus as well as scarred corneas and corneal transplants.
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: These tiny plastic inserts are surgically 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.
C3-R (corneal collagen cross-linking with riboflavin): This investigational, non-invasive procedure involves placing eye drops containing riboflavin (vitamin B2) on the cornea, which are then activated by ultraviolet (UV) light to strengthen links between the connective tissue (collagen) fibers within the cornea.
Studies of the C3-R procedure have shown promising results. In one small German study, progression of keratoconus was stopped in all of the 23 eyes studied. Most patients also had some reversal of keratoconus and minor vision improvement. Researchers concluded that this simple method of treatment might significantly reduce the need for corneal transplants among keratoconus patients.
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 successful cornea transplant, most keratoconic patients still need glasses or contact lenses for clear vision.