Impact of Time of Day on Dry Eye Disease: Findings from a Large Dry Eye Clinic Cohort.

Introduction: Previous research on the influence of time of day on dry eye disease (DED) symptoms and tear film characteristics has yielded inconsistent results, despite frequent reports of diurnal fluctuation in patient-reported symptoms. This study aimed to clarify these temporal patterns by evaluating both subjective and objective measures of DED in a large clinical cohort. Methods: A total of 1044 patients from a Norwegian dry eye clinic were assessed between September 2021 and December 2023. Associations between time of day and both subjective symptom scores and objective clinical parameters were evaluated using Pearson correlation, while diurnal rhythmicity was assessed using single-component cosinor analysis with a fixed 24-hour period. Results: Patients reported increased symptom severity in the morning and evening. However, analyses demonstrated statistically significant but clinically negligible correlations between time of day and all measured objective tear film parameters. No meaningful diurnal variation was identified in quantitative clinical metrics. Discussion: These findings reveal a persistent disconnect between subjective symptom patterns and objective clinical measures in DED. The lack of clinically meaningful diurnal variation in tear film parameters suggests that time of day may have limited relevance for objective assessment, while symptom variability may be driven by factors not captured by standard clinical testing. Further research is needed to better understand the mechanisms underlying this discrepancy.