Phospholipids and their degrading enzyme in the tears of soft contact lens wearers

Purpose: Low tear phospholipids levels are associated with tear film instability in soft contact lens wearers. We assayed levels of phospholipids and their degrading enzyme secretory phospholipase A(2) (sPLA(2)) both in tears and deposited on contact lenses composed of 2 hydrophilic materials after 1 day of routine use. Methods: Polymacon (Medalist; FDA group 1, low water/nonionic) and Etafilcon A (One Day Acuvue; group 4, high water/ionic) contact lenses were worn for 12 hours by 16 experienced contact lens wearers. Phospholipids in tear fluids and deposited on contact lenses were estimated by phosphorus determination with ammonium molybdate through enzymatic digestion. Double-anti body sandwich ELISA was used to determine group IIa sPLA(2) concentrations, and sPLA(2) activity was assayed using 1,2-diheptanoyl thiophosphatidylcholine as substrate. Results: Phospholipids concentrations in tears with Polymacon and Etafilcon A were 186 +/- 39 and 162 +/- 33 mu g/mL, respectively. The latter concentration was significantly lower than that observed in the same subjects when not wearing contact lenses (P = 0.0023). In tears, both group IIa sPLA(2) concentrations and enzymatic activity remained unchanged, regardless of lens wearing. However, Etafilcon A (0.57 +/- 0.09 mu g/lens) showed more group IIa sPLA, deposition than Polymacon (0.01 +/- 0.01 mu g/lens; P < 0.001). Furthermore, group IIa sPLA(2) deposited on Etafilcon A but not on Polyrnacon lenses retained its enzymatic activity. Conclusion: Significant differences of group IIa sPLA(2) deposition were found in the 2 lenses tested. Such deposition might induce phospholipid hydrolysis in tears and thereby promote tear film instability in hydrophilic contact lens wearers.