The relative risk of ulcerative keratitis among users of daily-wear and extended-wear soft contact lenses: a case-control study

The authors performed a case-control study with 86 case patients, estimating separately for hospital-based and population-based controls the relative risk of ulcerative keratitis among users of extended-wear as compared with daily-wear soft contact lenses. The relative risk of ulcerative keratitis for extended-wear as compared with daily-wear lenses among the population-based controls was 3.90 and among the hospital-based controls, 4.21. Thirty-eight percent of those with extended-wear lenses used them only during the day, and 11 percent of those with daily-wear lenses occasionally wore them overnight. When lens wearers were distinguished according to their overnight use of lenses, the users of extended-wear lenses who wore them overnight had a risk 10 to 15 times as great as the users of daily-wear lenses who did not.