Eye Dryness During Sleep: Causes and Mechanisms
Eye dryness during sleep occurs primarily due to incomplete eyelid closure (lagophthalmos), reduced tear production during sleep, decreased blink rate or absence of blinking, and evaporative loss from the ocular surface—all of which disrupt the tear film's ability to maintain adequate lubrication of the cornea and conjunctiva. 1
Primary Mechanisms During Sleep
Eyelid-Related Causes
- Lagophthalmos (incomplete eyelid closure during sleep) is a major cause of nocturnal dry eye, allowing continuous tear evaporation and exposure of the ocular surface throughout the night 1
- Eyelid malposition, exophthalmos, and thyroid-associated ocular disease prevent complete lid closure during sleep 1
- Neuromuscular disorders affecting eyelid function (Parkinson disease, Bell's palsy) impair proper lid closure and blinking mechanisms 1
Tear Film Dysfunction
- Meibomian gland dysfunction causes increased tear evaporation by altering the quality of the oily lipid layer that normally prevents evaporation, which becomes particularly problematic during prolonged eye closure 2
- Reduced or absent tear production during sleep hours, especially in patients with aqueous deficiency, leaves the ocular surface inadequately lubricated 2, 3
- Tear film instability is more common than pure aqueous deficiency and represents the primary pathophysiologic mechanism 1, 4
Sleep-Related Factors
- Sleep disorders themselves are associated with dry eye disease, with studies showing 17.5% prevalence of dry eye among patients with sleep disorders 1
- Use of sedative-hypnotic medications for sleep disorders may be associated with dry eye development 1, 4
- Poor sleep quality shows a significant positive correlation with severity of dry eye disease 5
- Decreased sleep quality can aggravate dry eye symptoms by increasing tear osmolarity and decreasing tear production 5
Contributing Risk Factors That Worsen Nocturnal Symptoms
Medication Effects
- Antihistamines, antidepressants, and antianxiety medications reduce tear production and worsen overnight dryness 1, 4
- Anticholinergics and diuretics decrease tear secretion through disruption of efferent cholinergic nerves 1, 4
- Systemic retinoids (isotretinoin) significantly reduce tear production 1, 4
Environmental Factors
- Low humidity environments from air conditioning or heating increase evaporative loss during sleep 1, 4
- Direct air flow to the face during sleep (fans, HVAC vents) accelerates tear evaporation 1
Systemic Conditions
- Sjögren's syndrome causes destruction of lacrimal gland tissue, eliminating reflex tearing and severely reducing tear production during all hours including sleep 1, 4
- Diabetes mellitus, particularly with poor metabolic control, is associated with increased dry eye prevalence 1, 4
- Autoimmune thyroid disease and rheumatoid arthritis increase dry eye risk 1, 4
Clinical Pitfalls to Recognize
- Rosacea can be difficult to diagnose in darker skin tones and children, but significantly exacerbates nocturnal dry eye through meibomian gland dysfunction 1
- In younger patients and males with nocturnal dry eye, suspect underlying systemic or local conditions rather than age-related changes 1
- Extended screen time before bed reduces blink rate and worsens overnight symptoms by destabilizing the tear film prior to sleep 1, 4
- Frequent use of preserved eye drops (>4 drops daily) causes corneal epithelial breakdown that manifests as morning dryness 1, 4
Pathophysiologic Cascade
The lacrimal functional unit dysfunction leads to an unstable tear film that causes ocular irritation and potential epithelial damage 4. During sleep, this is compounded by: