Ultrastructural effects of topical timolol on the rabbit cornea. Outcome alone and in conjunction with a gas permeable contact lens.

Corneal epithelial erosions developed in two patients wearing gas permeable contact lenses (Boston) soon after commencing topical timolol maleate therapy. This prompted the following investigation. Forty rabbit corneas were examined by scanning and transmission electron microscopy after treatment for one month with one of the following: timolol ophthalmic solution, preservative-free timolol, contact lens, contact lens and timolol, contact lens and preservative-free timolol, contact lens and saline, or no treatment. Corneas treated with either timolol or contact lens alone showed mild to moderate edema or degeneration of epithelial and endothelial cells. However, the combined use of a contact lens and timolol produced marked alterations in both the corneal epithelium and endothelium.