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Editors Selection IGR 7-1

Clinical Examination Methods: 24-h IOP monitoring

Comment by Syril Dorairaj & Marcos Pereira Vianello on:

61386 Estimation of 24-Hour Intraocular Pressure Peak Timing and Variation Using a Contact Lens Sensor, Liu JH; Mansouri K; Weinreb RN, PLoS ONE, 2015; 10: e0129529

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The search for a continuous intraocular pressure (IOP) monitoring device to replace Goldmann applanation tonometer (GAT) remains a holy grail in ophthalmology. As the only modifiable parameter for treating glaucoma, a precise and continuous measurement of IOP is imperative. A perfect continuous monitoring device would be comfortable, easy to use in office and outside in home settings, noninvasive, economical, accurate, reproducible and should be in mmHg for comparison.

Although some studies have pointed that 24-hour rhythm is unaffected by nocturnal awakening in healthy individuals, it is certainly uncomfortable, anti-physiological and expensive to evaluate IOP changes in sleep lab settings. Recently, a wireless contact lens sensor (CLS) for 24-hour IOP monitoring was developed. It provides continuous monitoring of IOP, with good tolerability.

In the present study, Liu and colleagues compared the 24-hour IOP monitoring curve in 30 healthy volunteers. The pneumatonometer was used in one eye and the contralateral eye was fitted with a CLS that monitored circumferential curvature in the corneoscleral region related to the change of IOP. Although there is no algorithm that connects the CLS signals (in minivolts) to IOP values (in mmHg), the study tried to verify the correlation between estimates of IOP peak timing and IOP variations obtained by the two methods. The authors based their study on the principle that in healthy adults, 24-hour IOP rhythms in paired eyes are relatively symmetrical.

The authors tried to answer two questions in the study. Firstly, is the simulated peak timing based on 24-hour CLS data close to the 24-hour pneumatonometer peak timing? Secondly, do the simulated variations of the CLS 24-hour data correlate with the 24-hour variations of IOP data of the paired eye?

Both groups detected the mean peak timing outside office hours, during the sleep period. The results pointed out that the 24-hour CLS data showed simulated peak timing close to the 24-hour IOP peak timing obtained using the pneumatonometer. However, the CLS output signal amplitude did not correlate with the amplitude of pneumatonometer IOP in the contralateral eye, confirming the difficulty to establish a conversion formula from the CLS mV data to mmHg.

Advances in CLS technology in continuous monitoring of IOP has potential for changing the diagnosis and management of glaucoma. Contact lens sensor provides a good estimation of the habitual IOP peak timing but at this time further clinical trials are needed to demonstrate its validity in evaluating IOP variation.

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