Over 13 million people in the United States wear
soft contact lenses for refractive correction.
Ulcerative keratitis is considered the most serious adverse effect of the use of
contact lenses. We performed a case-control study with 86 cases patients, estimating separately for hospital-based (n = 61) and population-based (n = 410) 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 (95 percent confidence interval, 2.35 to 6.48) and among the hospital-based controls, 4.21 (95 percent confidence interval, 1.95 to 9.08). 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, and the users of daily-wear
lenses who sometimes wore them overnight had 9 times the risk of the users of such
lenses who did not. For the users of extended-wear
lenses, the risk of
ulcerative keratitis was incrementally related to the extent of overnight wear. A reduction in risk associated with more frequent attention to lens hygiene was almost significant. We conclude that
soft contact lenses worn overnight carry a significantly greater risk for
ulcerative keratitis than soft
lenses worn only during the day.