Purpose: As lipid fouling is a prevalent issue with silicon hydrogel materials, a novel, in vitro, study was conducted to mimic the adsorption of major tear film lipids over 20 days of extended wear. This study may give clearer insight into the rate of accumulation of lipid during the wear.
Methods: Commercial balafilcon A (Purevision), galyfilcon A (Acuvue Advance), lotrafilcon A and B (Night & Day and O2Optix) and senofilcon A (Acuvue Oasys), were all soaked overnight, in the dark, at 34.5oC in either cholesterol (0.5µg/mL; Avanti) or phosphotidylethanolamine (PE, 1.1µg/mL; Molecular Probe), both tagged with FITC. All solutions were made up in phosphate buffered saline (PBS) at pH 7.2. The lenses were then washed 3 times in PBS and fluorescence was measured using the Wallac 1420 and calculated off an appropriate standard curve. The lenses were then placed into a fresh 1mL of the lipid being tested and the protocol was repeated for 20 days.
Results: Adsorption of cholesterol was greater for all lens types compared to PE. After 20 days of soaking in PE lotrafilcon A and B showed the lowest adsorption, of 0.4 and 1.5µg/lens, respectively. Galyfilcon A and senofilcon A showed significantly higher PE adsorption of 5.1 and 4.9 µg/lens respectively. Balafilcon adsorbed 3.2µg/lens of PE.
Balafilcon A had the highest affinity for Cholesterol with a significantly greater adsorption of 24.1µg/lens compared to all other lens types after 20 days. Lotrafilcon B showed the lowest adsorption of cholesterol at 3µg/lens. Adsorption of both polar and non-polar lipids reached saturation with senofilcon A and galyfilcon A at approximately day 12. Lotrafilcon A and B plateau at approximately day 17. Balafilcon showed greater affinity for non-polar lipids compared to polar lipids. Saturation of adsorption of PE occurred by day 14, whereas saturation was not complete with cholesterol by day 20 with balafilcon.
Conclusions: Lipid adsorption varied greatly depending upon the lens material for both polar and non-polar lipids. Overall, there was less adsorption of lipid to the lotrafilcon polymers indicating that hydrophobicity of the silicone elastomer drives adsorption and may be retarded by a uniform surface treatment such as that found on lotrafilcon A and B.