Tear lipid degradation during overnight contact lens wear

Abstract

Purpose: To examine the differences in lipids deposits from worn silicone hydrogel materials (Balafilcon A and Lotrafilcon A) worn daily vs overnight. The deposits were analysed using Gas Chromatography Mass Spectrometry (GCMS). Method: Single lenses were extracted in chloroform: methanol (1:1) and transmethylated prior to analysis by GCMS. The lenses used were collected from a clinically controlled study (n=30) where lenses were worn daily or continuously for 30 days. Results: Lotrafilcon A lenses (16:0 average peak height 112 Kcounts) accumulated much less lipid than Balafilcon A (16:0 average peak height 1213 Kcounts). Results also showed a significant difference in lipid profile from lenses worn on a daily wear basis compared to those worn on a continuous wear basis and this was shown to be irrespective of lens material. The lenses that were worn daily for a month accumulated more unsaturated lipid such as C16:1 and C18:1. The lenses which had been worn continuously for the same period of time had little to no unsaturated fatty acids. Conclusions: Although atmospheric oxidation of lipids occurs during daily wear of contact lenses, oxidation of lens-immobilised lipids during successive periods of overnight wear is even more dramatic. The fact that lenses worn on an overnight basis for 30 days yielded predominately saturated lipids suggests that unsaturated lipids are oxidised during eye closure. This correlates with the known increase in inflammatory mediators in the overnight tear film and indicates a marked increase in free radical production leading to the degradation of unsaturated lipids.