Pellucid Marginal Degeneration is a sub-category of keratoconus. Pellucid corneas involve a larger distorted area than keratoconus. 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 quite challenging.
Typically a larger gas permeable lens is necessary in order to achieve adequate vision and comfort. Smaller lenses tend to be very unstable on a pellucid cornea and may move significantly on the cornea with each blink causing a great deal of irritation.
Very often, scleral lenses are what works best on these types of corneas. Scleral lenses vault the entire cornea and are supported by the white portion of the eye (the sclera). The space between the back surface of the lens and the front surface of the cornea is filled with tears and saline solution. 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 outstanding. The great majority of patients are able to wear their scleral lenses almost all of their waking hours without problems.