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Results from an observational study of patients wearing silicone hydrogel contact lenses showed that subjectively rated vision or comfort deteriorate during the day and toward the end of the wearing period.
Dr. Dumbleton added that the study also provided evidence that enhanced compliance favored better outcomes. Recommended replacement frequency played a role as well, with results favoring patients who switched lenses just once a month compared with those on a 2-week replacement schedule.
"We know that many patients are poorly compliant about changing their contact lenses according to the recommended replacement frequency, and we were interested in investigating the role of compliance on the subjective comfort and vision of [SiHy] lenses. Our results suggest that clinical performance of these newer-generation contact lenses is enhanced by better compliance," said Dr. Dumbleton, senior clinical scientist, Centre for Contact Lens Research, University of Waterloo, Canada.
"The findings on the effect of replacement frequency may seem counterintuitive," she continued. "Perhaps there is some bias in which some patients are preferentially given a more frequent lens replacement schedule. However, this was an uncontrolled observational study and there are a number of unaccounted for factors. Ideally, we would like to perform a large controlled study, but we recognize that would be very difficult to conduct."
The data on comfort and vision were derived from a study designed for the primary objective of investigating compliance with replacement frequency. It enrolled 1,389 patients seen at 158 eye-care practitioners' offices, including 741 patients wearing 2-week replacement lenses and 648 patients in lenses with a 1-month replacement frequency.
During a routine office visit, patients were given a survey asking them to rate lens comfort and vision in the morning when they inserted their lenses and in the evening when they removed them. They also were asked to compare new lenses and ones that were ready to be replaced. The ratings were made on a scale of 0 (poor) to 10 (excellent).
"A possible limitation of our study was that patients were not given specific instructions on completing the survey," she said. "Furthermore, perhaps the simple rating scale we used was not an optimal tool for assessing subjective performance."
There were no significant differences between the 2-week and 1-month replacement frequency groups with regard to gender distribution, mean age, average number of days that lenses were worn per week, or the average hours worn per day.
Criteria for noncompliance
Noncompliance was defined as a replacement interval of 18 days or longer for the 2-week wearers and >1 month for the 1-month wearers. Using these criteria, the noncompliance rate was about twofold higher among 2-week wearers compared with patients in 1-month replacement lenses, 59% versus 29%.
Older patients were more likely to be compliant with their replacement schedule than younger patients. The difference between age groups was small but statistically significant. There was no gender-related difference in compliance, she said.