Despite having been around for more than a decade and the convenience they offer, less than 8 per cent of contact lens prescriptions are extended wear (EW), according to a study reported in the February issue of Optometry and Vision Science, the official journal of the American Academy of Optometry.
The study was based on an analysis of worldwide prescribing data, led by Nathan Efron, BScOptom, PhD, DSc, of Queensland University of Technology, Australia.
Researchers analysed data on contact lens fittings by eye care professionals in 39 countries from 1997 to 2010 and trends in EW contact lens prescribing, including patient characteristics and fitting patterns.
The data suggested that use of EW lenses peaked in 2006, when they accounted for 12 per cent of all soft contact lens prescriptions. However, the rate subsequently decreased, falling to 7.8 per cent in 2010. The rate varied between countries, ranging up to 27 per cent in Norway.
EW prescribing…is unlikely to become a mainstream lens wearing modality until the already low risks of ocular complications can be reduced to be equivalent to that for daily wear
Certain groups of patients were more likely to receive EW lenses, including men, older patients, and those not receiving their first contact lens prescription (“refits”) – patients who are experienced with contact lenses—and perhaps better able to afford the higher cost of EW lenses. Additionally, the researchers speculate, some men may prefer EW lenses because of their convenience for sports participation.
Most patients with EW lenses used some form of lens care solution, which suggested they remove and store their lenses at least occasionally, rather than wearing them full time for the entire month. Nearly 30 per cent of EW lens prescriptions were for conventional hydrogel lenses – possibly because they are less expensive than newer silicone hydrogel lenses designed specifically for 30-day extended wear.
Safety Concerns Are Key Issue
Dr. Efron and colleagues believe safety concerns are probably the key factor behind the limited acceptance of EW lenses. The first EW lenses introduced to the market were associated with high complication rates. These problems were mostly eliminated by the current generation of oxygen-permeable silicone hydrogel lenses.
The rate of severe keratitis with modern EW lenses is low, around 20 cases per 10,000 lens wearers per year. However, that’s higher than the four per 10,000 annual rate for daily contact lens wearers. Dr. Efron and coauthors conclude, “EW prescribing…is unlikely to become a mainstream lens wearing modality until the already low risks of ocular complications can be reduced to be equivalent to that for daily wear.”
