In-eye performance of soft contact lenses made from different materials

The in-eye performance of soft contact lenses may be affected by the material from which they are fabricated and may alter during wear. This study describes clinical and laboratory experiments that were conducted in order to examine the in-eye performance of eight soft contact lenses manufactured from different materials; these materials (and nominal water contents) were: HEMA/VP 40%, HEMA/VP 55%, HEMA/VP 70%, VP/MMA 55%, VP/MMA 70%, HEMA 40%, HEMA/MAA 55% and HEMA/MAA 70% (HEMA: 2-hydroxy-ethyl methacrylate, VP: vinyl pyrrolidone, MMA: methyl methacrylate, MAA: methacrylic acid). Two lenses from each of the eight soft contact lens groups were used in experiments concerning their parameter stability. Six subjects were fitted with lenses for 1 day. Verification of back optic zone radius, total diameter, back vertex power, centre thickness and water content was undertaken at 20 degrees C. In vitro measurements of total diameter were taken at 35 degrees C before lens fitting and after 6 h of lens wear. In vivo measurements of lens centration, up-gaze lag, post-blink movement, total diameter and subjective assessment of comfort were taken (a) immediately after lens insertion (1 min), (b) 20 min later and (c) 6 h later (same day). The majority of differences of the in vivo parameters between lens types (with respect to lens centration, lag, movement on blink, lens total diameter and comfort) were not found to be statistically significant throughout the 6 h wearing period. It was also found that lenses increase in diameter when first placed on the eye and decrease in diameter when they were removed from the eye. The information generated in study concerning the in-eye performance of soft contact lens materials may assist the contact lens industry and contact lens practitioners in developing and prescribing soft lenses with optimal performance characteristics.