Corneal ectasia is a condition resembling keratoconus but comes from a different origin. Almost invariably the cause is refractive eye surgery, specifically LASIK. After LASIK, the cornea has been made thinner. Because the corneal “wall” has been made thinner, internal pressure from within the eye can cause expansion or distension of the cornea.
The resultant distorted corneal surface will usually make it impossible to have clear vision with eyeglasses or soft contact lenses. Most of the time a special gas permeable contact or scleral lens will be needed to restore lost vision.
These special high tech lenses (which have only recently become available) will act to create a new corneal surface allowing the patient to regain clear, comfortable vision.
Pellucid Marginal Degeneration
Pellucid Marginal Degeneration is a sub-category of keratoconus. Pellucid corneas involve a larger distorted geographic area usually extending from the inferior corneal margins up to the center of the cornea. It is not unusual for 50% or more of the corneal surface to be involved. Because so much of the cornea can be affected, fitting this type of cornea can be more challenging.
The problem we face as eyecare practitioners is fitting the steep areas if the cornea without adversely affecting the flatter areas. Typically what is needed is a much larger gas permeable lens than would be used when fitting a “nipple” cone. Smaller lenses tend to be very unstable on a pellucid cornea and may wobble on the cornea with each blink causing a great deal of irritation.
Very often, even the larger lenses will not work and we are forced to use a gas permeable scleral lens. Scleral lenses vault the entire cornea and are supported by the white portion of the eye (the sclera). A special liquid fills the space between the back surface of the lens and the front surface of the cornea. This liquid acts as a buffer and protects the compromised corneal tissue. These lenses are almost always very comfortable and the vision provided by them is extremely good. The great majority of patients are able to wear their scleral lenses almost all of their waking hours without problems.
Vision Loss and Corneal Transplant Surgery
Many keratoconus patients fear that their keratoconus will keep on progressing causing further vision loss or ultimately corneal transplant surgery. This is not necessarily true. There have been many new advances in contact/scleral lens technology. This has allowed the overwhelming majority of keratoconus (ectasia, pellucid marginal degeneration) patients to wear these specialty lenses safely, comfortably and with good to excellent vision for almost all of their waking hours. Please understand that for the overwhelming majority of keratoconus patients, the active progressive stage of this disease seldom exceeds 5 years. I have seen many keratoconus patients over a 30 year period have virtually little or no change in the status of their corneas.
Corneal transplant surgery is not without risk. Infection and/or rejection of the graft can occur. In addition, the long term use of anti-inflammatory drugs used after this surgery can have undesirable side effects. The great majority of the post-corneal transplant patients who I have seen over the years have had irregularly curved corneas which required the use to special gas permeable contact lenses to restore useful vision. The fitting of a contact lens on a transplanted cornea can be even more challenging than on a keratoconic cornea.
To sum up, everything should be done to avoid a corneal transplant. Every year, new materials and technologies are appearing to make it easier for the keratoconus patient to be fit so as to allow better vision and comfort while maintaining ocular health.
A few words about Hydrops:
Hydrops is a rare complication of keratocunus, generally occurring in advanced keratoconus. It is caused by a fissure or split within the internal layers of the cornea. Fluid then enters the cornea from within the eye. When it occurs, the cornea becomes acutely swollen and opaque (cloudy/white).
There is no specific treatment. The condition will clear over a period of several weeks to months. The cloudy vision should improve over time. Hydrops typically results in corneal scarring. If the split is in the central part of the cornea, vision may be impaired, no matter what type of correction is attempted. Occasionally, hydrops can benefit keratoconus patients who have extremely steep corneas. As the cornea heals, a flattening of the cornea often results, making it easier to fit with a contact or scleral lens.
When hydrops causes extreme pain and/or light sensitivity, scleral lenses should be fit as soon as possible. This is because the scleral lens promotes healing and protects the irritated corneal tissue. In addition, vision and comfort is usually very good.
Developing hydrops in one eye does not necessarily mean that you will develop it in the other eye. Keratoconus, is often a very asymmetrical condition in that one eye is often much more advanced than the other.
Corneal Collagen Crosslinking treatment for Keratoconus and Post-Lasik Ectasia.
Collagen Crosslinking (CXL) has been shown to be an effective treatment for Keratoconus and Post-Lasik Ectasia. While not yet approved by the FDA, the 512 patient multicenter U.S. trial study has been completed and FDA approval is expected in 2014.
This minimally invasive in office procedure is intended to strengthen the Collagen Fibers that give the Cornea it’s shape and stability. Studies have shown that the Cornea does strengthen but the process can take 6 months to a year. The intent of the procedure is to prevent further progression of the Keratoconus or Ectasia. In a minority of cross-linking patients, there has been evidence of Regression of the Keratoconus.
Collagen Crosslinking involves the installation of and saturation of the Cornea with Riboflavin Eyedrops followed by the Precisely Timed application of a Beam of UV-A Light to strengthen the mechanical properties of the Cornea. At the present time there are two methods of performing CXL. One involves the removal of the Corneal Epithelium (the outer layer of the Cornea) and the other procedure leaves the Corneal Epithelium intact. At the present time studies are being done to determine which method is more effective.
The bottom line on Collagen Crosslinking is that after all is said and done, the patient will still need to wear their Specialty Contact or Scleral Lenses.