| Abstract: | Background : Wearing a hydrogel contact lens disrupts tear film stability, resulting in a low non-invasive surface drying time (NISDT) on the lens front surface. Reduced wettability causes deposit formation, reducing the quality of vision and lens comfort. This investigation determined the effect of commercially available HEMA-based materials on pre-lens tear film stability and deposition. Methods : Twenty patients in a randomised, double blind study wore four lenses for eight hours. These lenses were Tefilcon, Polymacon (Group I lenses), Vifilcon A and Etafilcon A (Group IV lenses). Non-invasive surface drying time (NISDT) was measured for each lens type after 10 minutes, one hour, four hours and eight hours wear. Lenses were then removed and examined by scanning electron microscopy. Results : NISDT decreased significantly (p < 0.05) over the eight-hour wear period for all lens types. Group IV lenses showed a slightly, but not clinically significantly, higher NISDT compared to Group I lenses. A greater number of deposits was seen on Vifilcon A and Polymacon compared to Etafilcon A and Tefilcon lenses. Conclusions : Wear decreases lens wettability over eight hours, irrespective of lens type. Higher wettability was seen with Group IV lenses, although the increase was not clinically significant. Wettability was not correlated with the formation of discrete deposits. Deposit formation depends on the composition of the lens base material, its ionic charge, surface topography, water content and wearers' ocular characteristics. |
