PURPOSE. With a trend towards longer wearing times for daily-wear contact lenses, and the re-emergence of extended wear with silicone hydrogel lenses, there is a distinct need for products that will help maintain cleanliness of lenses during wear. Objective measurement of deposit removal by in-eye rewetting drops is difficult. This study was designed to develop and test spectroscopic methods to evaluate protein removal of in-eye lens rewetting products. METHOD. Attenuated total reflectance -- Fourier transform infrared (ATR-FTIR) spectroscopy was used to measure surface protein on worn hydrogel (etafilcon A) and silicone hydrogel (balafilcon A) lenses. In-eye cleaning was simulated with a brief dip and agitation in either plain buffered saline or in one of two rewetting products (RW-1, Allergan, or RW-2, Alcon), followed by a second FTIR analysis. UV spectrophotometry was then used to measure the amount of protein released into the test product.
RESULTS. The ATR-FTIR technique indicated 1% to 10% reduction in surface protein following rewetter treatment on both types of lenses. There were no statistical differences in protein signal between rewetting products. The UV absorbance measurements indicated significantly greater protein release with RW-1 than with RW-2; however, products containing an ingredient with high UV absorption (out to 300 nm) gave anomalous results. ATR-FTIR surface protein levels were similar between lens materials, but UV analysis showed higher protein removal from the hydrogel lenses.
CONCLUSIONS. ATR-FTIR and UV spectroscopy are complementary techniques for measuring protein accumulation and removal from contact lenses. ATR-FTIR confirmed surface protein cleaning, but precision is affected by spectral contributions of the lens polymer and water. UV spectroscopy measured protein removal with greater precision. Differences in protein recovered suggest protein is more easily removed from hydrogel materials, or that some protein is removed from regions below the 1-micron measurement depth of ATR-FTIR. Differences in protein removal between solutions may have clinical relevance.