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Editors Selection IGR 24-3

Clinical Examination Methods: Diurnal IOP patterns

Comment by Andrew Tatham on:

92798 24-h intraocular pressure patterns measured by Icare PRO rebound in habitual position of open-angle glaucoma eyes, Fang Z; Wang X; Qiu S et al., Graefe's Archive for Clinical and Experimental Ophthalmology, 2021; 259: 2327-2335

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Intraocular pressure (IOP) varies over time, exhibiting instantaneous, diurnal-nocturnal, short-term, and long-term fluctuation.¹ Diurnal-nocturnal fluctuation is normal, with seminal sleep laboratory studies showing that even factoring for increases in IOP in the supine position, the majority of individuals have higher IOP at night.² There is also evidence for dysregulation of normal circadian IOP rhythms in glaucoma³, and growing evidence that IOP fluctuation may be a risk factor for glaucoma progression.¹ Fluctuating IOP can also make it difficult to determine therapeutic effect and set appropriate treatment targets.⁴

This study examined 24-hour IOP curves in 30 patients with primary open-angle glaucoma and 30 healthy controls using a rebound tonometer (RT) (ICare PRO, ICare Finland). Patients were admitted to hospital and IOP was measured every two hours, including overnight, using the RT and a non-contact pneumotonometer (NCT) (Full Auto Tonometer TX-F, Canon, Japan). Whereas the RT allowed IOP to be measured in the habitual body position (supine at night, sitting during the day), the NCT only permitted measurements when sitting.

The results showed good agreement between RT and NCT measurements in the sitting position during the day, with 95% limits of agreement of -2.1 to 3.4 mmHg for healthy subjects. RT measurements were higher than NCT measurements during the night due to RT measurements being taken when supine. Consistent with other studies, IOP was found to be higher at night in both healthy participants and in those with glaucoma. However, patients with glaucoma had higher IOP, greater IOP fluctuation, earlier IOP elevation in the nocturnal period, and greater IOP change from supine to sitting position.

The study provides further evidence of dysregulation of IOP rhythm in glaucoma and confirms the findings of previous sleep laboratory studies in observing higher IOP at night and in the supine position. However, as patients did not undergo a medication washout, it is not clear whether findings would be replicated in untreated eyes. Further limitations include the variety of IOP lowering medications used, the choice of NCT rather than Goldmann applanation tonometry as the reference standard, and that NCT measurements were taken only in the sitting position. In addition, no information was provided regarding corneal biomechanical properties, and their potential effect on differences between devices, and all IOP measurements were taken in hospital, so may not reflect IOP changes that occur during normal activities.

The study provides further evidence of dysregulation of IOP rhythm in glaucoma and confirms the findings of previous sleep laboratory studies in observing higher IOP at night and in the supine position

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