Testing hypotheses for risk factors for contact lens-associated infectious keratitis in an animal model.

Various risk factors contributing to contact lens related infectious corneal ulcers were tested. These factors included the presence of infectious organisms, loss of corneal surface integrity, and corneal hypoxia. High concentrations of Pseudomonas bacteria were applied to rabbit corneas under the following conditions: normal, intact corneal surface; "mild" corneal hypoxia with extended-wear soft contact lens and eyes closed; "moderate" corneal hypoxia with daily wear soft contact lens and eyes closed; "severe" corneal hypoxia with daily wear aphakic soft contact lens and eyes closed; corneal abrasion and eyes open; corneal abrasion and eyes closed; corneal abrasion with soft contact lens and closed eyes. No infectious ulcers occurred in normal intact corneas. The frequency of infectious ulcers increased with increasing degrees of corneal swelling. No ulcers were found in corneas with a mean swelling of 10%, whereas a mean swelling of 20% resulted in ulcers in half the group, and a mean swelling of 43% resulted in ulcers in all eyes. The three groups of abraded corneas resulted in infectious ulcers at a 20 to 30% frequency. The presence of infectious organisms alone does not lead to infectious corneal ulcers in rabbits. Corneal abrasions are a risk factor for infectious ulcers, but moderate and severe degrees of hypoxia are more significant.