What Causes Dry Eyes During Sleep
Incomplete eyelid closure during sleep (lagophthalmos) is the primary cause of nocturnal dry eye, allowing continuous tear evaporation and ocular surface exposure throughout the night. 1
Primary Nocturnal Mechanisms
Eyelid Closure Problems
- Lagophthalmos—the inability to fully close the eyelids during sleep—is the most important structural cause, permitting uninterrupted tear film evaporation for 6–8 hours overnight. 1
- Eyelid malposition, exophthalmos, and thyroid-associated eye disease mechanically prevent complete lid closure, creating persistent corneal exposure. 1
- Neuromuscular disorders (Parkinson disease, Bell's palsy) disrupt the motor pathways controlling lid closure and blinking, leaving the ocular surface vulnerable during sleep. 1
Tear Film Dysfunction
- Tear film instability—rather than pure aqueous deficiency—is the dominant pathophysiologic mechanism underlying nocturnal dryness. 1
- The tear film becomes more unstable overnight when reflex tearing is absent and environmental factors (low humidity, air flow) accelerate evaporation. 1
Sleep-Related Factors
- Sleep disorders themselves carry a 17.5% prevalence of dry eye disease, independent of other risk factors. 1
- Sedative-hypnotic medications (including benzodiazepines) used to treat insomnia may worsen dry eye through anticholinergic effects that reduce tear secretion. 1
Medications That Worsen Overnight Dryness
- Antihistamines, antidepressants, and antianxiety medications reduce tear production via anticholinergic pathways, compounding overnight symptoms. 1
- Anticholinergics and diuretics disrupt efferent cholinergic nerves that stimulate lacrimal secretion, decreasing tear volume during sleep. 1
- Systemic retinoids (isotretinoin) markedly suppress tear production, leading to severe morning dryness. 1
Environmental Factors During Sleep
- Low humidity from air conditioning or heating accelerates evaporative loss from the ocular surface throughout the night. 1
- Direct air flow to the face (fans, HVAC vents positioned near the bed) dramatically increases tear evaporation while asleep. 1
Systemic Conditions Contributing to Nocturnal Dry Eye
- Sjögren's syndrome destroys lacrimal gland tissue, eliminating reflex tearing and causing severe overnight dryness. 1
- Diabetes mellitus, especially with poor glycemic control, increases dry eye prevalence and worsens nocturnal symptoms. 1
- Autoimmune thyroid disease and rheumatoid arthritis elevate dry eye risk through inflammatory mechanisms that persist during sleep. 1
Pre-Sleep Behaviors That Aggravate Morning Symptoms
- Extended screen time before bed reduces blink rate and destabilizes the tear film prior to sleep, priming the ocular surface for overnight desiccation. 1
- Frequent use of preserved eye drops (>4 drops daily) causes corneal epithelial breakdown that manifests as pronounced morning dryness. 1
Clinical Pitfalls to Recognize
- Rosacea can be difficult to diagnose in darker skin tones and children, yet significantly exacerbates nocturnal dry eye through meibomian gland dysfunction. 1
- In younger patients and males presenting with nocturnal dry eye, suspect underlying systemic or local conditions (thyroid disease, neurologic disorders) rather than attributing symptoms to age-related changes. 1
- Symptoms typically peak upon waking, improve later in the morning, then worsen again toward evening—this diurnal pattern reflects the cumulative effects of overnight exposure and daytime environmental stressors. 2