If eyes are not properly lubricated during sleep (during REM sleep the eyes move quickly causing aqueous tears to be secreted by the lacrimal glands and meibum to be secreted from the meibomian glands), when we open our eyes for the first time in the morning, our lids may be stuck to our eyes.
Aqueous tear deficiency or meibomian gland dysfunction (MGD) can cause the eyes to stick to the lids because the protective barrier created by the tear film is compromised.
Lagophthalmos, a condition where the eye does not close completely, can cause the lids to stick to the eyes because the lubricating tear film can evaporate during sleep.
Infections can cause eye lids to stick to the eyes.