Risk Factors for Corneal Infiltrative Events with 30-Night Continuous Wear of Silicone Hydrogel Lenses

Nancy Keir - PhD OD - Centre for Contact Lens Research, University of Waterloo, Waterloo

Nancy Keir is currently a Research Associate at the Centre for Contact Lens Research at the University of Waterloo in Ontario, Canada, where she is responsible for conducting clinical research in the areas of contact lenses and refractive surgery. She graduated with honours in Optometry from the University of Waterloo and is currently working towards her MSc Degree in Vision Science on a part-time basis.

Risk Factors for Corneal Infiltrative Events with 30-Night Continuous Wear of Silicone Hydrogel Lenses

McNally J, Chalmers R, McKenney C, Robirds S.

Eye and Contact Lens. 2003 Jan; 29(1):S153-S156.

When prescribing silicone hydrogel (SH) lenses to be worn on a continuous wear (CW) basis, it’s important that we learn as much as we can about the risks involved. One of our greatest fears, of course, is the risk of microbial keratitis (MK), which can lead to severe vision loss. Previous research has shown that the greater the lens Dk/t the lower the amount of Pseudomonas binding to the epithelial cells. ¹ Subsequently, we would expect the incidence of MK to decrease with SH lens wear compared with lower Dk/t hydrogel lenses. This doesn’t eliminate the risk of MK, however.

Research has shown that risk factors for corneal infiltrates are similar to those for MK, and could provide insight into predicting which individuals are more susceptible. 2 In the January 2003 issue of Eye and Contact Lens (CLAO Journal), John McNally et al. discuss the results of a study investigating the risk factors associated with infiltrative events for up to 30-nights of continuous wear of lotrafilcon A lenses. This information should be useful for practitioners, in the selection, counselling and management of CW patients.

The study was a prospective, randomized 1-year clinical trial including 658 participants from 59 clinical sites in the United States. Participants were healthy adults over, with a mean age of 34.5 years, and included neophytes (12%) and successful hydrogel lens wearers who had worn their lenses on either a daily wear (47%) or extended wear (40%) basis. Seventy percent of participants were women, 90% were Caucasian and 15.7% were smokers. Lenses were worn for up to 30 nights of extended wear and were examined at the end of the wearing cycle. Five percent of participants experienced at least one infiltrative event.

The study found no association between infiltrative events and previous lens types or wearing schedule, refractive error, sex, lens fit, lens wear experience or baseline corneal neovascularization. There was no significant difference in risk between smokers and non-smokers, though the risk for smokers under 30 years of age was 2.7 times greater than the risk among nonsmokers under 30. No increased risk was found for smokers 30 years or older.

Approximately eight percent of those under 30 experienced an event compared with 3.7% of those 30 years or older. The indication of a prior inflammatory episode, such as a small corneal scar or a history of contact lens acute red eye (CLARE), was also associated with an increase in risk: 18.5% of those who entered the trial with corneal scars developed infiltrates, whereas only 4.5% of those without scars developed an event. History of CLARE was associated with a nearly 7 times increase in risk of developing an event. Finally, 10 (30.3%) out of the 33 participants who experienced an event experienced a second infiltrative event during the course of the study. This meant that those who experienced a first event were nearly 6 times as likely to develop a second event.

These findings are particularly interesting and extremely important for counseling and managing patients in CW. This study suggests that individuals should be closely monitored during the first month of wear, as this is when the majority of inflammatory events were found to occur. Additionally, those who experience an inflammatory event, or have a history of an inflammatory event, should be carefully counseled regarding their risk for a second event. Young patients, and young smokers in particular, should also be counseled about their increased risk. Most importantly, since the majority of events were found during unscheduled visits, all patients wearing lotrafilcon A lenses should be advised to return for care immediately if they experience any noticeable change in comfort, vision, or the appearance of their eyes.

It is our obligation as eye care practitioners to be as up-to-date as possible about all the vision correction options available to our patients. CW with silicone hydrogel lenses is a very exciting opportunity to provide patients with constant, reversible correction with very low risk. Studies of this nature play an important role in the development and implementation of new products, such as lotrafilcon A lenses, helping determine the best candidates for CW and how patients should be managed. Applying the result of this study in the practice can help to reduce this risk even further. In time it will be interesting to determine what other factors might play a role as the market experience with this lens grows and more long-term studies have been conducted. With such important information being uncovered, be sure to stay tuned…

1. Ren DH, Petroll WM, Jester JV, Ho-Fan J, Cavanagh HD. The relationship between contact lens oxygen permeability and binding of Pseudomonas aeruginosa to human corneal epithelial cells after overnight and extended wear.CLAO J. 1999 Apr;25(2):80-100.

1. Cutter GR, Chalmers RL, Roseman M. The clinical presentation, prevalence, and risk factors of focal corneal infiltrates in soft contact lens wearers. CLAO J. 1996 Jan;22(1):30-7.