Purpose: To understand the association of lipid biochemistry on lipid layer function during short term contact lens wear.
Methods: Fifteen participants with healthy eyes and no prior contact lens wear were recruited. The sample size was calculated based on a pilot study of evaporation rates with a standard deviation of 5.6 g/m2h to detect a difference between groups at 0.5% significance level with 80% power. The study was conducted in two randomized stages without and with contact lens wear (Ciba Vision, Focus Dailies, -0.50 D).Tear evaporation rate from both eyes was measured using the VapoMeter (Delfin Technologies, Finland) and basal tears were collected. Tear evaporation rate and tear collection were performed at the end of 6 to 8 hours of contact lens wear or similar time with no lens wear. Differences in tear evaporation rate between lens wear and no lens wear were compared using a paired t-test and associations between evaporation rate and concentration of phospholipids in tear film lipid layer were assessed using a Pearson correlation coefficient.
Results: The mean pre-corneal evaporation rate was 94.3±43.3 g/m2h and this was significantly lower (p<0.01) than the mean pre-lens evaporation rate was 126.7±46.1 g/m2/h. There was a strong association (R2 =0.85,p<0.05) between evaporation in the lens wearing and non-lens wearing eye. After 6-8 hours of lens wear, there was a weak but significant inverse association between the evaporation rate and the concentration of total phospholipids (R2=0.25 p=0.03) and total lysophospholipids (R2=0.29 p=0.02) in the tear film lipid layer.
Conclusions: Tear evaporation rate was consistently higher during contact lens wear than without lens wear. Higher evaporation rates were associated with reduced phospholipids in tears indicating a potential role of phospholipids in lipid layer function.