Editors Selection IGR 20-3

Pathogenesis: IOP and Posture

John Liu

Comment by John Liu on:

81419 Posture-Dependent 24-Hour Intraocular Pressure Fluctuation Patterns in an Intraocular Hypertension Monkey Model, Tu S; Li K; Hu D, Translational vision science & technology, 2019; 8: 63

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Non-human primates are superior to any other animal species to study anatomical characteristics related to human glaucoma. Since elevated intraocular pressure (IOP) is the most important risk factor for glaucoma and a laser induced glaucoma model using rhesus monkeys is available, an important issue is the timing and the magnitude of IOP elevation in this model. While a snapshot measurement of IOP does not represent the dynamic nature of IOP, periodical IOP measurements during a 24-hour period may determine daily timing of IOP peak. The current report is a comprehensive study on the posture-related IOP changes during a 24-hour period using this experimental model. Measurements of IOP were taken immediately and ten-minute after changing to the supine position as well as immediately and ten-minute after changing to the sitting position. Comparisons were made between glaucomatous monkeys and carefully matched healthy monkeys. The authors reported that IOP levels in the glaucomatous monkeys were always higher than those in healthy monkeys in all study parameters. Short-term and long-term IOP fluctuations during the 24-hour period were also larger in the glaucomatous monkeys. Critically, results showed that 24-hour IOP pattern had its highest IOP during the diurnal/wake period in these glaucomatous monkeys. Timing for the largest postural-dependent IOP changes also occurred during the diurnal/wake period. As the authors acknowledged, all the IOP measurements in this study were under anesthesia following intramuscular injections of ketamine and chlorpromazine. These agents probably eliminated normal posture-related responses in the cardiovascular and neuronal systems in conscious monkeys. In this regard, how significant is the gap between real life and the experimental conditions affecting IOP fluctuation is unclear. Therefore, it is important to verify the observations in the current report using conscious monkeys with implanted pressure transducers to monitor IOP. In addition, one should not forget the difference in natural sleeping postures for rhesus monkeys (usually sitting) and humans (recumbent) when considering the real-life 24-hour IOP patterns in habitual body positions.

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