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Purpose: This study investigated independent risk factors and causative organisms in microbial keratitis in daily disposable contact lens (CL)-wearers., Methods: A multisite prospective case-control study was undertaken. Cases were daily disposable CL-wearers attending Moorfields Eye Hospital with microbial keratitis and those reported through a one-year surveillance study in Australia and in New Zealand. A population-based telephone survey identified daily disposable CL-wearing controls. Subjects completed a questionnaire describing CL-wear history, hygiene and demographics. The sample used for risk factor analysis was weighted in proportion to the CL-wearing population at each location. Corneal scrape results were accessed. Independent risk factors were determined using multiple binary logistic regression. Causative organisms in different CL-wear modalities were compared using a chi-squared test., Results: 963 daily disposable CL-wearers were identified, from which 67 cases and 374 controls were sampled. Independent risk factors were; wearing CLs every day compared with less frequent use (OR 10.4x; 95% CI 2.9-56.4), any overnight wear (OR 1.8x; 95% CI 1.6-2.1), less frequent hand washing (OR 1.8x; 95% CI 1.6-2.0), and smoking (OR 1.3x; 95% CI 1.1-1.6). Certain daily disposable CLs (OR 0.2x; 95% CI 0.1-0.2) had protective effects. Environmental organisms were less frequently recovered with daily disposable CLs (20%), compared with other modalities (36%; p<0.02)., Conclusion: Overnight wear, increased exposure in daily wear, smoking and poor hand hygiene are significant risk factors for microbial keratitis with daily disposable CLs. Risk varied with daily disposable CL type. The profile of causative organisms is consistent with less severe disease.

Purpose: To assess the relative risks of acute, nonulcerative complications with recently introduced contact lens (CL) wear modalities (compared with the previously most common soft lens wear schedule), and to identify any other associated factors., Design: A 2-year prospective case-control study commencing in December 2003., Participants: Cases were 877 CL wearers attending Moorfields Eye Hospital with CL-related disorders other than microbial keratitis. Controls were 1069 hospital controls who were CL wearers presenting with a disorder unrelated to CL wear, and 639 population-based controls who were CL wearers randomly selected from the Moorfields catchment area. Hospital patients completed a self-administered questionnaire; population controls were interviewed by telephone., Testing: The relative risks of developing the CL-related disorders with different CL types were evaluated. For the more common disorders, multivariable analysis was undertaken., Main Outcome Measures: The relative risk of developing an acute, nonulcerative, CL-related disorder., Results: Compared with planned replacement soft CL, daily disposable lenses significantly reduced the risk of toxic/hypersensitivity (odds ratios for CL solution disorders and papillary conjunctivitis 0.1 and 0.5; P<0.001 and P = 0.05, respectively) and metabolic disorders (0.4; P=0.04), but the most commonly used brand was associated with increased risks of sterile keratitis (2.7x; 95% confidence interval [CI], 1.7-4.1; P<0.001), mechanical disorders (2.2x; 95% CI, 1.5-3.2; P<0.001), and a tendency for patients to have lens removal difficulties (P<0.001). Silicone hydrogel CL wear was free from hypoxic complications but associated with an increased risk of sterile keratitis (2.0x; 95% CI, 1.2-3.3; P=0.005), mechanical disorders (1.8x; 95% CI, 1.1-2.8; P=0.015), and attendance with any nonulcerative complication (1.9x; 95% CI, 1.5-2.6; P<0.001) when compared with other reusable soft lenses. Significant additional risk factors were identified for sterile keratitis (overnight wear [ON], more days per week of lens wear, poor hand hygiene, smoking, and less CL experience) and mechanical disorders (ON and less CL experience)., Conclusions: Neither of the 2 recently introduced CL modalities-daily disposable and silicone hydrogel lenses-reduced the overall risk of acute nonulcerative disorders.

Objective: To assess the relative risks (RR) of microbial keratitis (MK) for contemporary contact lens (CL) types and wearing schedules., Design: A 2-year prospective case-control study begun in December 2003., Participants: Cases were 367 CL wearers attending Moorfields Eye Hospital with proven or presumed MK. Controls were 1069 hospital controls, who were CL wearers with a disorder unrelated to CL wear, and 639 population-based controls who were CL wearers randomly selected from the Moorfields catchment area. Hospital patients completed a self-administered questionnaire; population-based controls were interviewed by telephone., Testing: Multivariate analysis was done both for all cases of MK, and for the moderate and severe MK subgroups alone., Main Outcome Measures: The RR for developing MK, and vision loss, for all lens types compared with planned replacement soft lenses (the referent)., Results: Compared with planned replacement soft lenses (the referent), the RR of MK was significantly increased with daily disposable (DD) CLs (RR, 1.56x [95% confidence interval (CI), 1.1-2.1]; P = 0.009) and differed between different brands of DD lens, was reduced for rigid lenses (RR, 0.16x [95% CI, 0.06-0.4]; P<0.001), and no different for silicone hydrogel or other types of soft lens. Although the risk of MK was higher overall among DD lens users, the risk of vision loss was less than for planned replacement soft CL users (P = 0.05); no DD lens users lost vision to the level of >or=20/40. The RR for overnight wear, for any lens type, was 5.4 times higher (95% CI, 3.3-10.9; P<0.001). Comparison of the DD soft CL types with planned replacement soft lenses (the referent), showed significant differences between brands for the risk of MK., Conclusions: The risk of MK has not been reduced in users of DD and silicone hydrogel CLs. However, vision loss is less likely to occur in DD than in reusable soft CL users. Different brands of CL may be associated with significantly different risks of keratitis; understanding these differences should lead to the development of safer soft lenses. These findings suggest that lens/ocular surface interactions may be more important in the development of corneal infection than oxygen levels and CL case contamination.

Objective: To investigate reasons for an increase in cases of Acanthamoeba keratitis related to contact lenses., Design: Case-control study. Cases were contact lens related acanthamoeba keratitis patients treated between 1 September 1989 and 31 August 1992. Controls were lens users without lens related disease who presented as new patients to the casualty department from 1 March 1992 to 31 August 1992. All subjects completed a questionnaire detailing lens use and hygiene practices., Setting: Eye hospital., Subjects: 35 cases with acanthamoeba keratitis and 378 controls., Main Outcome Measures: Relative risks comparing different contact lens types, socioeconomic classification, age, sex, lens use, lens wearing experience, hygiene compliance, and hygiene systems., Results: The crude relative risk for developing acanthamoeba keratitis with the use of daily wear disposable lenses was 49.45 (95% confidence interval 6.53 to 2227; P < 0.001) compared with conventional soft lenses (the referent). Multivariable analysis showed that this increased risk could be largely attributed to lack of disinfection (relative risk 55.86 (10 to 302); P < 0.001) and use of chlorine based disinfection (14.63 (2.8 to 76); P = 0.001) compared with other chemical systems (the referent). None of the other outcome measures showed a significant association., Conclusions: Both failure to disinfect daily wear soft contact lenses and the use of chlorine release lens disinfection systems, which have little protective effect against the organism, are major risk factors for acanthamoeba keratitis. These risks have been particularly common in disposable lens use. Over 80% of acanthamoeba keratitis could be avoided by the use of lens disinfection systems that are effective against the organism.

A case-control study was used to evaluate the relative risk (RR) of acute contact lens-related disorders. The study sample comprised new patients wearing contact lens presenting at the accident and emergency department at Moorfields Eye Hospital, London, England, in 12 months. Disorders were classified by pathogenesis. Compared with gas-permeable hard contact lenses (the referent), extended-wear soft contact lenses were related to the largest overall RR for any complication (2.7 [95% confidence limits, 1.73, 4.16]), whereas for daily wear soft contact lenses the overall RR was 1.3 (confidence limits, 1.0, 1.72). Relative risks were greatest for extended-wear soft contact lens wearers with metabolic disorders (2.1 [confidence limits, 1.28, 3.4]) and for such wearers with sterile infiltrates (2.4 [confidence limits, 1.22, 4.84]). Among those using daily wear contact lenses, RR was highest for those with toxic/hypersensitivity disorders (5.9 [95% confidence limits, 3.27, 10.49]). Severe complications involving greater morbidity occurred more frequently with extended-wear soft contact lenses. This could be reduced by selecting a more appropriate lens type to correct low refractive errors.

Microbial keratitis is a potentially binding disease that is rare in normal eyes unless associated with contact lens (CL) wear. To assess the risks of CL use, and other major causes, for keratitis, a case-control study of 91 cases of keratitis including 60 CL users was done. Relative risks (RR) and population attributable risk percentages (PAR%) for keratitis were estimated for different causes and for the different types of CL. The RR (95% confidence intervals) for CL wear was 80 (38-166) and for trauma cases 14 (6-32) compared with cases of keratitis without a predisposing condition. The PAR% for microbial keratitis attributed to CL wear was 65%. The RR for overnight wear soft lenses was 21 (7-60), for daily-wear soft lenses 3.6 (1-14), and for polymethylmethacrylate hard lenses 1.3 (0-9) compared with gas-permeable hard lenses. Continuous periods of CL wear for more than 6 days was associated with increased risk. CL wear is now the commonest cause, and has the highest risk, for new cases of microbial keratitis at Moorfields Eye Hospital. Soft CLs, especially extended-wear lenses, carry a significantly higher risk than do hard lenses for this disease.

Ninety four patients with 'sterile' keratitis presenting consecutively over a nine month period to the Accident and Emergency Department of Moorfields Eye Hospital were studied. This condition was found to account for 0.49% of all new casualties. A significant association was found in these patients, compared with controls, with contact lens hygiene, particularly for daily wear soft contact lenses, and contact lens case contamination by bacteria suggesting that these may be important factors in the aetiology of 'sterile' keratitis. Compared to gas permeable hard contact lenses the relative risk of developing 'sterile' keratitis in our patients was found to be 2.3 times higher with extended wear soft contact lenses, 1.56 times higher with daily wear soft contact lenses and 0.509 with polymethylmethacrylate lenses (test of trend p-value less than 0.05). The results indicate that 'sterile' corneal infiltrates are related to contact lens hygiene and in part to contact lens case contamination by bacteria and also to the type of lens worn.