Abstract
Purpose: :
To evaluate the influence of air exposure during in vitro deposition of two model lipids on silicone hydrogel (SH) and conventional hydrogel (CH) contact lens materials, via a custom-designed model blink cell (MBC).
Methods: :
Four SH (balafilcon A "BAL"; lotrafilcon B "LOB"; comfilcon A "COM"; senofilcon A "SEN") and two CH (etafilcon A "ETA" and omafilcon A "OMA") contact lens materials were mounted on six pistons and placed in a controlled atmosphere chamber at 35°C with a relative humidity of 18%. The pistons were connected to a motor that cycled the contact lenses in and out of an artificial tear solution (ATS). Lenses were cycled for 10 hours; 2 seconds in the ATS then exposed to air for 5 seconds, which allowed the tear film to break over the surface of the contact lens. Control lenses were kept submerged for 10 hours. The ATS used contained lipids, proteins, mucin, salts and a trace amount of one of the radioactive lipids; 14C-cholesterol (C) or 14C-phosphatidylcholine (PC). Following incubation, each lens was extracted twice, evaporated under nitrogen, re-suspended in chloroform and then scintillation cocktail. Extracts were counted in a beta counter and raw data were translated into absolute amounts (ng/lens) via extrapolation from standard curves.
Results: :
For the two model lipids tested, SH lens materials deposited statistically more lipid than the CH lens materials, with BAL depositing the most lipid. Air exposure significantly increased the amount of C that deposited on BAL, OMA, COM, and SEN (p≤0.03). No change in deposition was seen for LOB and ETA (p>0.05). All lenses exposed to air resulted in increased amounts of PC deposited. These levels were statistically significantly higher (p<0.04) for LOB, SEN, COM and OMA, but not statistically significant (p>0.05) for BAL or ETA.
Conclusions: :
This model has demonstrated that lipid deposition kinetics can be impacted by air exposure and that lipid deposition profiles are contact lens dependent. In vitro models must begin to use more physiologically relevant incubation solutions and conditions that mimic contact lens wear within the natural tear film if in vitro data is to be extrapolated to the in vivo situation.
Keywords: lipids • contact lens