IOP fluctuates seasonally in healthy, glaucomatous eyes
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IOP fluctuated by season in patients with healthy eyes and primary open-angle glaucoma, with an increase in the winter and decrease in the summer, according to a study published in Ophthalmology Glaucoma.
“Elevated IOP is considered the most important and only clinically modifiable risk factor for the development and progression of glaucoma,” Ryo Terauchi, MD, of the department of ophthalmology at The Jikei University School of Medicine in Japan, and colleagues wrote. “At present, IOP reduction is the only proven treatment approach for glaucoma.”
Terauchi and colleagues conducted a retrospective, Kaplan-Meier survival analysis to evaluable seasonal fluctuations in retinal nerve fiber layer (RNFL) thinning and IOP in normal eyes and eyes with primary open-angle glaucoma (POAG). The study comprised 179 patients with POAG who were treated with glaucoma eye drops and underwent Goldmann applanation tonometry in the winter and summer. They had a follow-up of at least 3 years. Researchers also included a control group of 12,686 healthy eyes. They conducted the study in Tokyo, Japan, in 2019, with December through February considered the winter season and July through September the summer season.
The 179-person treatment cohort included 33 eyes with POAG and 146 with normal-tension glaucoma. The mean follow-up was 98.4 months; most patients were men who were 55.1 years old, on average. During the observation period from July to December 2019, 47.5% patients had significant RNFL thinning progression. The average rate of RNFL thinning was –0.44 m/year. Terauchi and colleagues found winter IOP significantly higher than summer IOP (13.0 ± 2.3 mm Hg vs. 11.9 ± 2.0 mm Hg; P < 0.001). The seasonal fluctuation was 1.13 mm Hg, and the fluctuation rate was 10%.
Among the nonglaucomatous patients, winter IOP was significantly higher than summer IOP (13.2 ± 3.0 mm Hg vs. 12.5 ± 2.9 mm Hg; P < .001). The researchers found the presence of disc hemorrhage, using more glaucoma eye drops, having a higher summer IOP and lower season fluctuation and being a woman were factors significantly associated with progressive RNFL thinning. However, when applying Cox proportional hazards model, they found the seasonal IOP fluctuation rate still significantly and negatively associated with RNFL thinning. Also, summer IOP exhibited a significant and positive association with thinning compared to winter IOP.
“In eyes with POAG, seasonal IOP fluctuation had a significant impact on the progression of RNFL thinning,” Terauchi and colleagues wrote. “A temporary IOP decline in summer, rather than a constant IOP throughout the year, may prevent glaucoma progression. This finding will serve as the foundation for more detailed assessments of the impact of seasonal IOP fluctuations on glaucomatous pathologic features.”
Perspective
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Terauchi and colleagues found that IOP varies seasonally, and a seasonal IOP drop may in fact be protective. That is surprising, as it is generally thought that stable IOP rather than fluctuating pressure prevents progression of glaucoma, at least in the short term.
While it has been theorized that ocular surface disease — more prevalent in winter — may have some connection to increased IOP, the cause remains unclear. The study also found that women have a greater risk for glaucoma progression.
As doctors we must be comfortable with the idea that despite our years of education and clinical experience, we will likely witness dramatic changes to the way we diagnose and treat glaucoma during our professional careers. We must stay humble and redouble our commitment to lifelong learning. It is also imperative not to mock patient’s “silly” theories outright or “unfounded” concerns because over time they may be proven right. It’s best to simply explain “this is not our understanding of the disease at this time.” During my almost 20-year career I have witnessed ideas that were once dismissed as impossible (or ridiculed as absurd) become the consensus.
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Terauchi R, et al. Ophthalmol Glaucoma. 2020;doi:10.1016/j.ogla.2020.11.005.
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