Large specialised sebaceous glands in the eyelid. There are about 50 glands on the upper lids and 25 glands on the lower lids. They create and distribute an oily substance called lipids. Meibomian gland secretions help keep the eye moist. When blinking, the upper lid comes down, presses on the oil and pulls a sheet of oil upwards, coating the tear layer beneath to keep it from evaporating.