Seasonal Fluctuation in Intraocular Pressure and Retinal Nerve Fiber Layer Thinning in Primary Open-Angle Glaucoma.

PURPOSE

To detect seasonal fluctuations in intraocular pressure (IOP) in healthy eyes and eyes with primary open-angle glaucoma (POAG) and to evaluate whether these seasonal fluctuations affect retinal nerve fiber layer (RNFL) thinning in eyes with POAG.

DESIGN

Observational, retrospective cohort study.

PARTICIPANTS

Healthy population who underwent a comprehensive health check-up and patients with POAG using only topical medications were enrolled.

METHODS

Kaplan-Meier survival analysis was used to compare the cumulative incidence probabilities of RNFL thinning between different seasonal IOP fluctuation groups. A Cox proportional hazards model, with adjustments for potential confounding factors, was used to evaluate the association between seasonal fluctuations in IOP and RNFL thinning.

MAIN OUTCOME MEASURES

Intraocular pressure fluctuation rate calculated from winter and summer IOPs and RNFL thinning as determined by event-based analysis with high-definition OCT.

RESULTS

A total of 12 686 healthy eyes and 179 eyes of 179 POAG patients showed a significantly higher IOP in winter than in summer (healthy, 13.2 ± 3.0 mmHg vs. 12.5 ± 2.9 mmHg [P < 0.001]; POAG, 13.1 ± 2.7 mmHg vs. 11.8 ± 2.3 mmHg [P < 0.001]). In POAG patients, the mean age at initial OCT and follow-up duration were 55.1 ± 11.7 years and 98.4 ± 26.4 months, respectively. The mean deviation (MD) at first visit, MD slope, and RNFL thinning rate were -2.2 ± 3.4 dB, -0.07 ± 0.44 dB/year, and -0.44 ± 0.88 μm/year, respectively. During the study period, 85 eyes (47.5%) showed RNFL thinning progression. Kaplan-Meier analysis showed that a high seasonal IOP fluctuation rate significantly suppressed RNFL thinning (P < 0.05, log-rank test). After adjusting for confounders in the Cox analysis, the seasonal IOP fluctuation rate still showed a significantly negative association with RNFL thinning (hazard ratio, 0.98; 95% confidence interval, 0.96-0.99; P = 0.005).

CONCLUSIONS

Winter IOP was higher than summer IOP in both healthy and POAG eyes. The temporary IOP decline in summer, rather than a constant IOP throughout the year, may prevent glaucoma progression.