Table 1. Total concentrations of the identified tear fluid lipid classes.

class	S1 (µM)	S2 (µM)	mean (µM)	STD (µM)
PC	13.8	28.0	20.9	10.1
PE	5.3	5.2	5.2	0.1
TG	1.7	1.3	1.5	0.3
Cer	1.1	0.8	0.9	0.2
SM	0.9	0.9	0.9	0.1
PS	0.1	0.1	0.1	0.0
TOTAL	22.9	36.3	29.6	9.5

The concentrations are based on the UPLC-MS data obtained from the analysis of samples S1 and S2. Cer, Ceramide; PC, phosphatidylcholine; PE, phosphatidylethanolamine; PS, phosphatidyl-serine; SM, sphingomyelin; TG, triglyceride; TOTAL, total lipid concentration.