Purpose: To investigate the diurnal secretory characteristics of individual meibomian glands (MGs).
Methods: Ten subjects (4 females and 6 males) with healthy eyelid appearance and without dry eye symptoms were recruited (mean age = 23.8 +/- 1.8 years). Both right and left lower eyelids were marked in 3 places to locate 5 consecutive MGs in each third (temporal, central, and nasal) of the lower eyelid. A total of 15 MGs per eye were diagnostically expressed for 10 seconds on both right and left lower eyelids every 3 hours for 4 consecutive measurements over a 9-hour period.
Results: Thirty-four percent of all tested MGs yielded liquid secretion at all measurements. Sixty-nine percent of the tested nasal MGs yielded liquid secretion at all measurements in contrast to 31% of the central MGs and only 22% of the temporal MGs. The mean numbers of MGs secreting liquid oil were significantly higher in the nasal section relative to the central and temporal sections at all measurements (p < 0.001, all measurements).
Conclusions: (1) A single MG is capable of secreting oil on demand over the course of a working day ( approximately 9 hours); (2) nasal MGs were the most likely to secrete upon demand over the course of day compared with the temporal and to a lesser degree the central MGs; and (3) secretory characteristics of individual MGs examined as a function of their location in the lower eyelid does not change diurnally.