Abstract
Abstract: :
Purpose: To determine the incidence and morbidity of keratitis among wearers of current generation contact lenses and to explore relevant risk factors. Methods: We conducted a 12–month, prospective, hospital–based epidemiological study in which the clinical severity of each presenting case of contact lens–associated keratitis was scored. The size and location of corneal infiltrates was documented. The hospital catchment population, and the wearing modalities (daily wear [DW] or extended wear [EW]) and lens types being used, were estimated from relevant demographic and market data. Risk factors were assessed using logistic regression analysis. Results: Over the 12 month survey, there were 38 cases of severe keratitis (SK; traditionally termed ‘microbial keratitis’) and 80 cases of non–severe keratitis (NSK). The annual incidence (cases per 10,000 wearers) of all forms of keratitis, SK and NSK among contact lens wearers was 21.3 (95% confidence interval 17.8 to 25.5), 6.9 (5.0 to 9.4) and 14.4 (11.6 to 18.0), respectively. The incidence of SK stratified for wearing modality and lens type was: DW rigid 2.9 (0.8 to 10.4); DW hydrogel daily disposable 4.9 (2.5 to 9.6); DW hydrogel (excluding daily disposable) 6.4 (4.1 to 9.9); DW silicone hydrogel 0.0 (0.0 to 210.1); EW rigid 0.0 (0.0 to 1759); EW hydrogel 96.4 (37.5 to 245.2); and EW silicone hydrogel 19.8 (6.7 to 58.0). The difference between EW hydrogel and EW silicone hydrogel was significant (p = 0.04). Corneal scrapes were performed in 23 cases of SK; 43% were culture–positive, with Pseudomonas aeruginosa identified as the main pathogen in 30% of cases. More infiltrates occur in the peripheral cornea with DW hydrogel lenses, in the central cornea with DW hydrogel daily disposable lenses and in the superior cornea with EW silicone hydrogel lenses (p < 0.05 in all cases). Infiltrative events that occur in the corneal periphery are less clinically severe. No patients suffered significant visual loss (95% confidence interval 0.0 to 9.4%). Significant risk factors in addition to lens type/modality were: gender, smoking, relevant eye and health problems, and season. Conclusions: There is a significantly higher incidence of severe keratitis in wearers who sleep in contact lenses. Silicone hydrogel lenses carry a 5X lower risk of severe keratitis for extended wear compared with hydrogel lenses. Overall, morbidity (visual loss) is low. Significant risk factors are identified but are of little predictive value.
Keywords: cornea: clinical science • clinical (human) or epidemiologic studies: prevalence/incidence • keratitis