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Editors Selection IGR 17-4

Clinical Examination Methods: Seasonal IOP Fluctuations I

Comment by Kaweh Mansouri on:

91626 Seasonal Fluctuation in Intraocular Pressure and Retinal Nerve Fiber Layer Thinning in Primary Open-Angle Glaucoma, Terauchi R; Ogawa S; Noro T et al., Ophthalmology. Glaucoma, 2021; 4: 373-381

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Terauchi et al. are to be congratulated for conducting a large-scale study to evaluate seasonal changes of IOP in healthy subjects and glaucoma patients and their effects on glaucomatous RNFL-thinning. Based on the monthly air temperature in Tokyo, winter period was defined as December through February and summer as July through September. Goldmann applanation tonometry was used for all measurements in the glaucoma group and RNFL thickness was measured using Cirrus OCT.

Including a total of 12 686 healthy eyes and 179 eyes of 179 POAG patients, the authors found a significantly higher IOP in winter than in summer in both subject groups. In glaucoma patients, winter IOP was significantly higher than summer IOP (13.0±2.3 mmHg vs. 11.9 ± 2.0 mmHg, in the progression vs the non-progression groups; P < 0.001). The progression group showed a higher summer IOP, lower seasonal fluctuation, and a lower seasonal fluctuation rate than the non-progression group. In healthy eyes too, winter IOP was significantly higher than summer IOP (13.2±3.0 mmHg vs. 12.5±2.9 mmHg; P < 0.001).

The progression group showed a higher summer IOP, lower seasonal fluctuation, and a lower seasonal fluctuation rate than the non-progression group.

Interestingly, the authors found that in eyes with POAG, seasonal IOP fluctuation had a significant impact on the progression of RNFL thinning. They posited that a temporary IOP decline in summer, rather than a constant IOP throughout the year, may prevent glaucoma progression.

Several factors may preclude generalizability of this studies results: (1) Most glaucoma patients were classified as NTG (81.6%), reflecting the particular epidemiological situation in Japan; (2) Patients presented a slow rate of visual field and RNFL progression. This may be due to the high proportion of NTG patients and also to the fact that patients with rapid glaucoma progression requiring laser or surgery were excluded; (3) Tokyo has a humid subtropical climate with intense seasonal fluctuation in air temperature. It would be interesting to know whether glaucoma patients in regions with more stable seasonal temperatures (e.g., San Diego, Beirut, Lisbon) present similar IOP fluctuations; (4) Although only office-hour IOP readings were available, a recent study by our group using an intraocular IOP sensor found similar seasonal 24-h IOP effects and confirmed their findings.¹

At present, the mechanism underlying seasonal IOP fluctuation remain unknown.

It would be interesting to know whether glaucoma patients in regions with more stable seasonal temperatures (e.g., San Diego, Beirut, Lisbon) present similar IOP fluctuations

In addition to external climate-related factors such as temperature and sun light, intrinsic biological factors may also be involved. For instance, higher endogenous cortisol may be one of the factors to explain the higher winter IOP. It is likely that a central mechanism and multiple factors including individual acclimatization may be involved that also explain why patients in warmer geographical locations do not seem to have lower IOPs than those in higher ones.

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