The role of different phospholipids on tear break-up time using a model eye

Purpose: The effect of different phospholipids in stabilising the tear film was investigated to determine if particular polar head groups gave greater stability than others. Methods: Purified phosphatidylcholine (PC), lysophosphatidylcholine (LPC), phosphatidylethanolamine (PE), phosphatidylglycerol (PG), phosphatidylserine (PS) and cardiolipin (CL) were used. These were applied to a model eye loaded with an artificial tear fluid and the tear breakup time (TBUT) was measured. Three variants of the artificial tear fluid were utilised: buffered saline alone; one with proteins and mucins; and one containing proteins, mucins and lipids. Results: TBUT was improved by the presence of phospholipids. In particular, the best performance was with PI applied to artificial tear fluid containing proteins mucins and lipids. Use of buffered saline as the artificial tear fluid gave very short break-up times. Conclusion: Increase in tear film stability by phospholipids is probably not due to the charge carried by the polar head group, but more likely due to the charge distribution, and the presence of hydroxyl groups in the head group also tends to increase stability, possibly through specific interactions with proteins and mucins in the subphase.