The Impact of Lipid on Contact Angle Wettability

PURPOSE: To analyze the effect of in vitro lipid doping on conventional hydrogel (CH) and silicone hydrogel (SH) lens wettability, assessed by sessile drop contact angle (CA) measurement. METHODS: Nine contact lens materials, five SHs and four CH, were incubated with two different lipid tear solutions (LTS) containing cholesterol, cholesteryl oleate, oleic acid, oleic acid methyl ester, and triolein. The first LTS was a "low" concentration solution, which was close to human values, and the second was a "high" concentration. Lenses were soaked in the two LTS types for 2 or 5 days and compared with lenses soaked in phosphate buffered saline (PBS) only. After soaking, advancing CAs were measured on a customized computerized device using a sessile drop method. RESULTS: Compared with PBS, CAs for untreated SHs were unaffected by soaking in the LTS, with typical CA values of >95 degrees (p > 0.05). The surface-treated SH materials exhibited markedly reduced CAs after lipid exposure, with the high concentration LTS reducing the CA to <5 degrees (p < 0.01). The CH materials all exhibited lower CAs after soaking, with values typically decreasing to 35 degrees , which was significantly lower than that seen with PBS (p < 0.01). CONCLUSION: Exposure to lipid may improve the wettability of certain SH and CH materials, particularly those SH materials that are surface treated. This may help to explain why certain SH materials appear to improve in comfort for some patients during the first few hours or days of wear.