The physiologic effects of extended wear soft contact lenses.

The major physiologic effect to the eyes of soft contact lenses in general and continuously worn hydrogel lenses in particular is a decrease in the amount of oxygen normally available to the cornea. This reduction in oxygen supply produces changes as minimal as clinically undetectable epithelial edema and as severe as the anoxic overwear syndrome that produces pain and decreased vision. Induced corneal edema can produce refractive error changes and endothelial cell changes. On a long-term basis the lenses produce physical trauma to the anterior surface of the cornea as well as certain metabolic changes and have been associated with a significant degree of corneal neovascularization. Because hydrogel lenses require a different type of care than standard, hard PMMA lenses, new complications are being described, such as giant papillary conjunctivitis, lens deposits, and acute red eye syndromes that may be associated with allergic or toxic reactions to preservatives used in the cleaning processes. Research is underway to develop hydrogel materials that will allow more oxygen to reach the corneal surface and prevent surface deposits from forming.