LC-MS/MS analyses of human meibum conducted in triple quadrupole mode. Ceramide (Cer), hexosyl ceramide (Hex-Cer), and sphingomyelin (SM) were separated by reverse phase LC using a C18 column, as described in the methods section. The mole percent of Cer, Hex-Cer, and SM were compared across groups defined by clinical parameters. A and B. Comparison of mole percent of Cer, Hex-Cer, and SM with meibum quality. C and D. Comparison of mole percent of Cer, Hex-Cer, and SM with meibomian gland dropout. E and F. Comparison of mole percent of Cer, Hex-Cer, and SM with inferior meibomian gland plugging.