If you've been told in the past that you cannot wear contact lenses because of an irregular cornea or other problems, you may want to get a second opinion and ask your eye doctor about scleral contact lenses.
Scleral contacts are large-diameter gas permeable contact lenses specially designed to vault over the entire corneal surface and rest on the "white" of the eye (sclera). In doing so, scleral lenses functionally replace the irregular cornea with a perfectly smooth optical surface to correct vision problems caused by keratoconus and other corneal irregularities.
Also, the space between the cornea and the back surface of a scleral lens acts as a fluid reservoir to provide comfort for people with severe dry eyes who otherwise could not tolerate contact lens wear.
Types Of Scleral Contact Lenses
There are three categories of scleral lenses, based on size and where the lenses have their primary contact with the front surface of the eye:
Corneo-scleral lenses and semi-scleral lenses are much larger larger than conventional GP lenses and rest near the junction between the cornea and the sclera.
Mini-scleral lenses vault over the entire corneal surface and rest on the anterior sclera.
Full scleral lenses are the largest scleral lenses and provide the greatest amount of clearance between the back surface of the lens and the cornea.
Typically, lenses that are 18 mm or smaller are subcategorized as mini-sclerals.The average human cornea is approximately 11.8 millimeters in diameter, so even the smallest scleral contacts are designed to cover the entire corneal surface.
In comparison, most conventional GP contact lenses are 9.0 to 9.5 mm in diameter and cover only 75 to 80 percent of the cornea.
Another category of gas permeable lenses bridges the size gap between conventional GP lenses and mini-sclerals. These lenses, called corneo-scleral lenses, generally are approximately 13 to 15 mm in diameter. Corneo-scleral lenses often are a good choice for people who require larger-than-normal GP lenses for greater comfort.
Anyway, during your contact lens exam and fitting, your eye care professional will determine the best scleral lens type and size for your specific needs.