contact lens materials
The Quest for All-Day Comfort
BY KATHY DUMBLETON, MSC, MCOPTOM, FAAO, & LYNDON JONES, PHD, FCOPTOM, FAAO
Despite the advances in contact lens materials over the past decade, patients are still dropping out of lens wear. One of the first comprehensive studies investigating contact lens drop out (Weed et al, 1993) reported that discomfort was the most common reason for ceasing lens wear. Six years later, Pritchard et al (1999) reported that of the contact lens patients who discontinued lens wear permanently, 49 percent did so because of discomfort symptoms.
Since these surveys were conducted, there have been significant changes in lens materials and wearing modalities, particularly with the widespread use of daily disposable and silicone hydrogel lenses. However, despite these changes, patients continue to cease contact lens wear as a result of discomfort (Richdale et al, 2007). Published studies to-date suggest that 22-to-24 percent of patients permanendy discontinue contact lens wear (Richdale, Sinnott et al, 2007)
Investigating Lens Discomfort
We recently conducted two studies at the Centre for Contact Lens Research to assess practitioner and patient compliance with recommendations for replacement frequency of daily disposable and silicone hydrogel lenses in the United States and Canada (Dumbleton et al, 2009; Richter et al, 2009). Daily wear patients reported wearing their lenses for 12 hours (Canada) to 13 hours (United States) each day, but 47 percent of patients in the United States and 55 percent of patients in Canada reported that their lenses became less comfortable later in the day. These numbers are depressingly close to those published in the 1990s.
Despite this discomfort, these patients reported continuing to wear their lenses for two-and-a-half hours beyond the time when the lenses became less comfortable. This seems to suggest that comfortable wearing time, even with current materials, is only about 10 hours per day for many patients, which unfortunately does not meet the lifestyle requirements for the majority of our patients today. Thus, it is not surprising that patients are still dropping out of lens wear.
Contact lens comfort is influenced by many factors other than lens material. Patient factors include age, gender, general health, systemic conditions, allergies, medications, diet, and the overall health of the eye and tear film. Lens factors include design, fitting characteristics, surface properties, and replacement frequency, in addition to lens material. Care products also play an important role for reusable lens types.
A study by Papas et al (2007) evaluated the effect of lens replacement during the day on contact lens-related discomfort. In this study, subjects wore nelfilcon A (Focus Dailies, CIBA Vision) lenses for nine hours on two separate days. They rated comfort during the day on both days, but on the second day the lenses were replaced with identical new lenses after five hours of wear. A progressive decrease in comfort during the day was reported on both days. Despite a transient improvement in comfort immediately after application of the new lenses after five hours on the second day, the end-of-day comfort ratings were the same as for the first day. The authors concluded that ocular factors rather than changes occurring in the lenses were more likely responsible for the discomfort resulting from lens wear.
The Quest Continues
The elusive quest for all-day comfort appears destined to carry on for some time. We will continue to see lens design and surface modifications to improve tear exchange and enhance comfort. Hopefully both will help our patients and result in materials that can offer enhanced comfort for longer wearing periods. CLS
For references, please visit www.clspectrum.com/references.asp and click on document #169.
Dr. Dumbleton is a senior clinical scientist at the Centre for Contact Lens Research in Ontario, Canada. Dr. Jones is the associate director of the Centre for Contact Lens Research and a professor at the School of Optometry at the University of Waterloo, Ontario, Canada. He has received research funding from Alcon, AMO, B&L, CIBA Vision, CooperVision, Johnson & Johnson, and Menicon.