Modern contact lens materials are prone to drying when exposed to air, which contributes to the buildup of deposits on contact lenses, according to a study -- "The Impact of Intermittent Air Exposure on Lipid Deposition," appearing in the November issue of Optometry and Vision Science, official journal of the American Academy of Optometry.

With significant differences between materials, the buildup of lipid deposits on contact lenses is affected by "intermittent air exposure" between blinks, according to Holly Loretz, PhD, and colleagues of the Centre for Contact Lens Research at University of Waterloo, Ont., Canada. The findings may help in developing new materials that are less prone to drying and lipid deposition -- thus increasing the chances of successful contact lens wear.

Air Exposure Leads to Increased Lipid Deposits on Contact Lenses The researchers built a new experimental setup, called the "model blink cell," to examine factors affecting the buildup of lipid (fatty) deposits on contact lenses. The model blink cell was designed to cycle contact lens materials in and out of an artificial tear solution containing trace amounts of cholesterol or other lipids naturally present in tear fluid.

To mimic the effects of routine lens wear, six different contact lens materials were subjected to simulated blinks and eyelid motion for varying periods. The researchers analyzed the effects of air exposure between "blinks" on the buildup of lipid deposits.

For most of the materials tested, air exposure led to increased lipid deposits. Compared to lenses that remained submerged in the artificial tear solution, the amount of cholesterol deposited on lenses was about three times greater with air exposure. For another type of lipid (phosphatidylcholine), lipid deposition was about 40 percent greater with intermittent air exposure.

Today's sophisticated contact lens materials have molecular characteristics related to "wettability" that seem to contribute to a cycle of lipid deposition that is encouraged by repeated wetting and drying. "This wetting/de-wetting cycle can occur after every blink and therefore thousands of times a day, thus allowing lipid to continuously accumulate on and in the lens material," Dr Loretz and coauthors write.

What does it all mean for contact lens wearers? "Contact lenses gather deposits during wear and contribute to discomfort and how successful the lenses are for the wearer," explains Anthony Adams, OD, PhD, Editor-in-Chief of Optometry and Vision Science. "Dry eyes can also negatively affect the chances of successful contact lens wear."

Although no laboratory model can fully simulate the effects of real-life contact lens wear, the model blink cell improves on previous approaches by accounting for the drying effects of intermittent air exposure. The effects of drying on lipid deposition may be even more important with today's sophisticated hydrophobic ("unwettable") lens materials.

"The model blink cell device allows clinical researchers to move beyond the current relatively simple in vitro models for studying deposits to a more real-life modeling of a contact lens on the eye, particularly with today's more hydrophobic silicon component hydrogel lenses," Dr Adams adds. "The authors are hopeful that this will allow research that could be expected to provide improved comfort in contact lens wear."