As with other comorbid conditions, like depression and anxiety which are more likely in people with DED, the directionality of this effect is complicated.
Poor sleep quality and dry eye are bidirectionally related. Depression, pain, and eye discomfort at night can worsen sleep, while poor sleep can worsen tear film quality and exacerbate symptoms.
Even one night of sleep deprivation can produce noticeable changes in tear film break-up time, tear osmolarity, and reduced tear secretion.
Similar effects have been observed in mice. Sleep deprivation decreased aqueous tear secretion, and increased corneal epithelial cell defects, sensitivity, and cell death.
Critically, however, these ocular surface changes were largely reversed following 2 weeks of rest.
The lacrimal gland, responsible for tear production, is regulated predominantly by parasympathetic (“rest and digest”) nervous system activity.
Sleep deprivation increases sympathetic nervous system activity. The commensurate decrease in parasympathetic tone therefore impairs lacrimation.
Conversely, dry eye symptoms can also lead to reduced sleep quality.
Topical treatment of dry eye improved overall sleep quality in DED patients that had been recently diagnosed, but not for those with longstanding DED.
Worsened sleep quality in severe DED is better correlated with mood, rather than the clinical parameters of DED (including the Schirmer test, tear break-up time, and keratoepitheliopathy).
As such, it may be that a psychiatric factor – likely, the distress caused by DED and dry eye symptoms – could be a major possible cause of impaired sleep quality.
Eye fatigue is another common DED symptom, likely caused by photophobia and tear film instability leading to blurred vision, which can also lead to distress and worsened sleep.