A: While contact lenses can help provide fantastic vision, they are essentially a foreign body to the eye and reduce oxygen flow to the ocular surface. Contact lenses have drastically evolved from the hard lenses that allowed no transmission of oxygen, to silicon-hydrogel lenses that allow great transmission. Nonetheless, as the lens ages, it dries and becomes less permeable. This, in turn, allows less oxygen to flow into the eye.
A two-week disposable lens worn for a month or two, while it may still feel comfortable on the eye, no longer allows adequate oxygen transmission. Deprived of oxygen, the eye will go through a process called neovascularization, in which new blood vessels grow into the cornea, bringing blood that will supply this tissue with oxygen. The cornea is naturally an avascular tissue, meaning that it is not supposed to have blood vessels in it and is meant to get oxygen through adjacent structures. If this neovascularization continues past a certain point, it is likely that contact lens use would have to cease indefinitely.
Sleeping in contacts is also a problem. Not only is the lens on the eye, but your eyes are also closed; thus there are two barriers to oxygen flow. If you find yourself mistakenly sleeping in your lenses multiple times a week, have your optometrist fit you in a contact lens approved for overnight wear. While overnight lenses allow the greatest amount of oxygenation, sleeping in any contact lens increases your risk of bacterial infection. This can ultimately result in inflammation, scarring, and vision loss.
Information provided by Dr. Matthew Ward, O.D. from Eye Care of Iowa, 5075 E. University Ave., Pleasant Hill 265-5322.