Seasonal Variation and Trend of Intraocular Pressure Decrease Over a 20-Year Period in Normal-Tension Glaucoma Patients.

PURPOSE:To investigate the trend of seasonal variation of intraocular pressure (IOP) in patients with normal-tension glaucoma over a 20-year period by retrospectively analyzing the Kyoto Prefectural University of Medicine Glaucoma Registry database as real-world data. DESIGN:Retrospective cohort study. METHODS:Data points (n = 49,007) were extracted retrospectively from the medical records of 1774 patients with normal-tension glaucoma (665 male patients and 1109 female patients; mean ± SD age was 59.8 ± 14.4 years; and mean ± SD observation period was 5.6 ± 4.4 years) seen over the 20-year period. We first calculated the mean IOP from all available data of each month from January 1997 through December 2016. The data were then categorized into 5 groups of 4 consecutive years each (1997-2000, 2001-2004, 2005-2008, 2009-2012, and 2013-2016) and the mean IOP of each month within the group was calculated. Seasonal variations of IOP over the 20-year study period and in the 5 consecutive groups were then investigated via nonlinear multiple regression analysis. RESULTS:A continuous decrease of IOP was detected throughout the 20-year period (P < .001), with distinct seasonal variation. The annual mean ± SD IOP was highest (13.9 ± 2.7 mm Hg) in the oldest group (1997-2000), with a gradual decrease in each subsequent group, finally becoming lowest (12.3 ± 2.7 mm Hg) in the most recent group (2013-2016) (P < .001), and all of them were accompanied by distinct seasonal variation (P < .001). CONCLUSIONS:Based on the Kyoto Prefectural University of Medicine Glaucoma Registry real-world longitudinal data, our findings revealed a continuous decrease and distinct seasonal variation of IOP in patients with normal-tension glaucoma throughout the 20-year study period.