Most of the focusing power in the eye occurs along the front surface, called the cornea, which is the clear "window" in the front of the eyeball. The next structure involved in focussing is the lens, which sits behind the cornea inside the eye. The ideal cornea has a round, symmetrically curved surface, like a basketball. Astigmatism is caused by an "out of round" cornea or a lens that is not symmetrical. As a result, people with significant astigmatism may have distorted or blurry vision.
Keratoconus is a condition in which the cornea (the clear, central part of the front surface of the eye) bulges outward like a cone. Normally, the cornea has a dome shape, like a ball. Sometimes, however, the structure of the cornea is just not strong enough to hold this round shape. Keratoconus can cause progressive deterioration of vision. Initially, keratoconus is treated with glasses, but often, contact lenses, first soft, then gas permeable, are necessary to allow the eye to see adequately. In approximately 10% to 15% of cases, however, medical management is insufficient, and surgery is necessary to improve vision.
How Are Intacs Used?
Intacs are clear plastic arcs that are designed to be inserted into the substance of the cornea in people who have keratoconus and who can no longer see properly with glasses or contact lenses. Intacs were approved by the FDA for treatment as an alternative to corneal transplant, which is a standard treatment for keratoconus.
When they are inserted into the eye, Intacs reshape the cornea by flattening it closer to its original dome shape. Although the procedure usually improves uncorrected vision, the patient will often still need glasses or contact lenses after the Intacs are inserted. After the cornea has been reshaped, patients who were once unable to tolerate contact lenses may be able to return to contact lens wear and see even better than they did with the lenses prior to surgery. Some patients may even be able to see well enough to go back to simply wearing glasses.