Lagophthalmos is a relatively common condition and is frequently overlooked as a key cause of or contributor to night dry eye symptoms.
What happens in lagophthalmos: When the lid does not fully seal, part of the cornea remains exposed and will dry out overnight. Even on a healthy eye this is a problem, but for someone who also has dry eye (whether evaporative dry eye or aqueous tear deficiency or both) this can often cause severe and dangerous drying at night, which can result in recurrent erosions, ulceration and eventually blindness in severe cases if not effectively treated.
What causes it: Lagophthalmos is a common side effect of cosmetic eyelid surgeries (blepharoplasty) and is also thought to be associated with LASIK laser eye surgery due to stretching with the speculum. Lagophthalmos can occur naturally. It is also associated with certain other conditions like thyroid disease; acoustic neuroma; and Bell's palsy.
What to do about it: Night eye protection is indispensable for people with nocturnal lagophthalmos. This can be done with anything from a simple sleep mask to the popular Tranquileyes moisture goggle. Often people with nocturnal lagophthalmos also need an effective lubricant in addition to eye covering, and humidification in the bedroom may be helpful too. Ceiling fans should be avoided and air ducts should be directed away from the eyes.
People with lagophthalmos during daytime too can benefit from moisture chamber glasses.