Keratoconus is a progressive eye disease in which the cornea thins and bulges into a cone-like shape, losing its roundness. The result is distorted vision.
Keratoconus can occur in one or both eyes. Keratoconus is relatively rare. If it does occur the onset usually begins in the teens or early twenties.
Symptoms of Keratoconus
Keratoconus may be difficult to detect and it typically develops slowly with few cases proceeding rapidly. As the cornea gradually becomes irregular in shape, progressively nearsightedness and irregular astigmatism increase. This creates problems such as distorted and blurry vision, glare and light sensitivity. Keratoconic patients often need prescription changes every time they visit their eye doctor.
Causes of Keratoconus
The weakening of the corneal tissue which leads to keratoconus appears to be from an imbalance of enzymes in the cornea. The enzyme imbalance makes the cornea susceptible to oxidative damage from free radicals, causing weakness and corneal bulge.
Risk factors for this type of oxidative damage and weakening of the cornea include genetic predisposition, which explains why keratoconus often affects multiple members of the same family. Keratoconus is also connected to ultraviolet (sun) overexposure, excessive eye rubbing, a history of poorly fit contact lenses along with chronic eye irritation.
For mild forms, eyeglasses or soft contact lenses help. As the severity of the disease progresses and the cornea thins and has an increasingly distorted shape, glasses or soft contacts will no longer provide adequate vision correction.
Treatments for moderate to advanced keratoconus include:
Rigid Gas permeable contact lenses. If eyeglasses or soft contact lenses cannot provide adequate vision, rigid gas permeable (RGP) contact lenses are usually effective. Rigid materials enable the RGP lenses to dome over the cornea, replacing the irregular shape with a smooth, uniform refracting surface, thus improving vision.
RGP contact lenses can be less comfortable to wear compared to soft lenses, but this improves as the eye gets used to the lenses. Fitting of the contact lenses on keratoconic corneas is also challenging and more time-consuming. Expect frequent office visits for fine-tuning and fitting of the prescription, especially as the keratoconus continues to progress.
Piggybacking lenses. Sometimes it is necessary to “piggyback” a soft contact lenses under the RGP contact lens if the RGP lenses are not comfortable. The soft lens acts as a cushion under the RGP lens.
Hybrid contact lenses. Hybrid contact lenses are a design combining highly oxygen-permeable rigid center with a soft peripheral lens “skirt.” These hybrid contacts may provide the crisp optics of RGP lenses with the comfort of soft contact lenses.
Scleral and semi-scleral lenses. These are RGP contact lenses which have a large diameter allowing the edge of the lenses to rest on the white part of the eye-the sclera instead of on the cornea. These lenses will also dome over the irregularly shaped cornea, providing good vision and allowing for a more comfortable wear. They also move less during eye blinks.
Intacs. These are tiny plastic inserts which are surgically inserted just underneath the eye surface in the periphery of the cornea helping to reshape the cornea. They should result in clearer vision. Intacs may be advised when keratoconus patients no longer can obtain functional vision with contact lenses or eyeglasses. The implants have the advantage of being removable and changeable. Intacs might delay, but will not prevent, a the need for a corneal transplant, if keratoconus progresses.
Corneal crosslinking. This procedure, “CXL” for short, strengthens corneal tissue which slows or improves the bulging of the eye surface. This procedure may reduce the need to undergo a corneal transplant.
There are two types of corneal crosslinking: epithelium-off and epithelium-on. Epithelium-off crosslinking is where the outer portion of the cornea (epithelium) is removed to allow entry of riboflavin, a B vitamin, to the cornea. Once administered, the riboflavin is activated with UV light. With the epithelium-on method (transepithelial crosslinking), the corneal surface is left intact.
Corneal transplant. Some people with keratoconus cannot tolerate a rigid contact lens, or they are beyond the point where contact lenses or other therapies provide acceptable vision. The last resort remedy may be a corneal transplant, also called a penetrating keratoplasty (PK or PKP). After a successful cornea transplant, most keratoconic patients will still need glasses or contact lenses for clear vision.