In a study published in BMC Ophthalmology, researchers conducted a meta-analysis to identify a potential association between sleep quality and dry eye.
Give me some background first.
Poor sleep quality and other sleep-related issues such as sleep disorders, insomnia, cardiac rhythm disorders, and excessive sleep have become ongoing global social issues.
In previous studies, it was shown that sleep disorders can lead to a higher risk of:
- Diabetes
- Hypertension
- Cancer
- Other adverse outcomes
And its connection to dry eye?
Dry eye is a multifactorial ocular surface disease (OSD) characterized by the following traits:
- Imbalance in tear film homeostasis
- Varying degrees of tear film instability
- Increased osmotic pressure
- Inflammation
- Nerve damage
Patients who have dry eye may experience poor sleep quality due to:
- Eye discomfort
- Incomplete eyelid closure
- Mental stress
Now, talk about the study.
In this meta-analysis, the researchers searched through several databases (PudMed, EMBASE, Cochrane, Web of Science, Grey literature) to find observational studies published before April 2023.
Two researchers independently screened all articles while a third researcher was consulted for resolution pending any disagreements. Data extracted included:
- Author or authors
- Country
- Study type
- Data collection period
- Publication year
- Dry eye type
- Participant numbers in dry eye and control groups
- Age
- Female proportion
- Sleep-related judgment criteria
Then what?
All the articles included underwent quality assessments based on their type.
For cohort and case-control studies, the Newcastle-Ottawa Scale (NOS) was used for assessment. The final scores were categorized as:
- Low quality (0 - 3 points)
- Medium quality (4-6 points)
- High quality (7-9 points)
For cross-sectional studies, the researchers used the Agency for Healthcare Research and Quality (AHRQ) scale for assessment. The final scores were categorized as:
- Low quality ( 0–3 points)
- Medium quality (4–7 points)
- High quality (8–11 points)
The researchers then performed a meta-analysis using STATA15 software.
Who was included in the study?
The researchers analyzed a total of 21 studies which included 419,218 participants.
The inclusion criteria for data used in the study included:
- Subjects aged 18+
- Case subjects diagnosed with dry eye or Sjogren’s syndrome (as long as diagnostic criteria were provided and the control subjects were healthy)
- Provision of the number of bad sleep quality or sleep scores for case and control participants
- Study type: observational research
Findings?
The researchers discovered that dry eye subjects experienced worse sleep quality when compared to healthy individuals, demonstrating:
- Poorer subjective sleep quality
- Longer sleep latency
- Higher risk of unhealthy sleep duration (such as insufficient sleep or excessive sleep)
Tell me more.
The Pittsburgh Sleep Quality Index (PSQI) scores of the dry eye patients were found to be significantly higher than the control participants.
The dry eye participants also scored higher than the control subjects in PSQI in the following categories:
- Sleep quality
- Sleep latency
- Sleep disturbance
The researchers found no significant difference between dry eye participants and control participants in PSQI scores in the following categories:
- Sleep duration
- Sleep efficiency
- Daytime dysfunction
- Sleep medication
Give me some numbers.
Lastly, it was found that participants with dry eye had:
- A significantly higher risk of sleep disorders than non-dry eye participants relative risk (RR) = 2.20, 95%CI: 1.78, 2.72, P < 0.001)
- A higher risk of insufficient sleep compared to control participants (RR = 3.76, 95%CI: 3.15, 4.48, P < 0.001)
- Higher rates of excessive sleepiness compared to control participants (RR = 5.53, 95%CI: 3.83, 7.18, P < 0.001)
- Significantly higher ESS scores compared to control participants (weighted mean difference [WMD] = 3.02, 95%CI: 2.43, 3.60, P < 0.01)
Limitations?
The researchers noted that most of the articles in their analysis utilized questionnaires to determine if patients suffered from dry eye or sleep disorders, which they stated have a certain degree of subjectivity.
They also mentioned that most of the articles were cross-sectional studies and provided little information regarding the mechanisms and relationships underlying the increased rate of sleep disorders found in dry eye participants.
And lastly?
Dry eye is more common in women and elderly participants—and the articles adjusting for the gender factor—more elderly women were included in the study population than other participants.
Expert opinion?
The researchers shared that their analysis confirms previous findings published in the Canadian Journal of Ophthalmology, which determined that dry eye patients are more likely to have a sleep disorder.
Further: They also noted that their research did not find a difference between dry eye patients and the healthy population in reference to daytime dysfunction (unlike the previous study findings).
And the potential reasons for this?
The researchers believe this discrepancy may be related to the sample size and subjectivity of the questionnaire in the prior study.
Lastly, the researchers recommended that for future studies: “More large-scale prospective studies are needed to provide more assistance in patient management and treatment.”
Take home.
While the study found that individuals with dry eye are more likely to have issues such as lower sleep quality and a higher risk of unhealthy sleep duration compared to the healthy population, there is lacking evidence to establish a causal relationship and related mechanisms between dry eye and sleep disorder.