The Impact of Incubation Conditions on In Vitro Phosphatidylcholine Deposition on Contact Lens Materials

SIGNIFICANCE Previous in vitro measurements of contact lenses commonly investigate the impact of nonpolar tear film lipids (i.e., sterols). Polar lipids, however, are equally important stabilizing components of the tear film. This research explores and presents further knowledge about various aspects of polar lipid uptake that may impact contact lens performance. PURPOSE This study evaluated the impact of incubation time, lipid concentration, and replenishment of an artificial tear solution (ATS) on the uptake of phosphatidylcholine (PC) onto conventional hydrogel (CH) and silicone hydrogel (SH) contact lens materials. METHODS Four SHs and two CH lens materials (n = 4) were soaked in a complex ATS containing radioactive C-14-PC as a probe molecule. Phosphatidylcholine uptake was monitored at various incubation time points (1, 3, 7, 14, and 28 days), with different ATS lipid concentrations (0.5x, 1x, 2x) and with and without regular replenishment of the ATS. Phosphatidylcholine was extracted from the lenses, processed, and counted by a beta counter, and accumulated PC (mu g/lens) was extrapolated from standard lipid calibration curves. RESULTS All materials exhibited increasing PC deposition over time. Conventional hydrogel materials showed significantly lower PC uptake rates (P < .001) than any of the SH materials. Increasing lipid concentration in the ATS resulted in increased PC binding onto the contact lens materials (P < .001). Replenishing the ATS every other day, however, impacted the PC deposition differently, showing increased binding (P < .001) on CHs and reduced PC deposition for SH materials (P < .001). CONCLUSIONS Length of incubation, lipid concentration in the ATS, and renewal of the incubation solution all influenced the amount of PC that sorbed onto various lens materials and therefore need to be considered when conducting future in vitro deposition studies.

Automated summary

This study examined the impact of incubation time, lipid concentration, and ATS replenishment on the uptake of phosphatidylcholine onto CH and SH contact lens materials. The results showed that all materials exhibited increasing PC deposition over time, with SH materials having higher uptake rates than CH materials. Increasing lipid concentration in the ATS resulted in increased PC binding onto the contact lens materials, while regular replenishment of the ATS showed different impacts on PC deposition for CH and SH materials.