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Editors Selection IGR 13-2

Clinical Examination Methods: 24-hour monitoring to detect Glaucoma Progression

Comment by Arthur Sit on:

107957 24-Hour Monitoring of Intraocular Pressure Fluctuations Using a Contact Lens Sensor: Diagnostic Performance for Glaucoma Progression, Gaboriau T; Dubois R; Foucque B et al., Investigative Ophthalmology and Visual Science, 2023; 64: 3

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Intraocular pressure (IOP) is highly variable and follows a distinct circadian rhythm with values higher during sleep than while awake when measured in the normal physiologic positions.¹ Secondary analyses of data from large clinical trials clearly show that increased IOP fluctuations between study visits is associated with increased risk of glaucoma progression, at least in some patient populations.^2,3 However, waiting months to years to assess IOP fluctuations is obviously not ideal for glaucoma management. The advent of new technologies for near-continuous IOP monitoring is providing a wealth of data, but how to interpret that data is still an emerging field. Gaboriau et al. performed an innovative study that analyzed 24-hour IOP profiles collected using the Triggerfish contact lens sensor (CLS; Sensimed, Etagnieres, Switzerland).

This prospective cohort study included 54 eyes of 54 open-angle glaucoma patients with at least two years of follow-up and five reliable visual-field tests using standard automated perimetry. CLS profiles were collected between May 2015 and May 2016, and subjects were divided into fast progressors (MD progression rate more than -0.5 dB/year) and slow progressors (MD progression rate less than or equal to -0.5 dB/year).

The CLS records voltage changes due to deformation of the cornea from IOP changes instead of IOP itself. Although the CLS records measurements every five minutes, each measurement is based on raw data consisting of 300 samples obtained over 30 seconds. Unlike most other CLS studies, this study used the raw data, with 24-hour profiles processed in three stages: (1) Removal of very short-term fluctuations (10 ms time scale) associated with blinks; (2) Adjustment for drift over the 24-hour period; and (3) Wavelet-based analysis to examine fluctuations over multiple different time scales ranging from 10 min to ≥4000 min. IOP profile fluctuations between the two patient groups were compared by examining the absolute area under the receiver operating curve (AUROC) from wavelet-based analysis. The authors found that fast progressors had higher AUROC for time scales of 24-hours and 60-220 minutes. There was no difference at a time scale of 120-500 minutes.

This study has significant strengths in the systematic approach provided by wavelet-based analysis. However, there are several potential weaknesses in the study. Most importantly, the two groups were not equivalent: the fast progressors had higher baseline IOP and more severe VF defects. Whether or not the 24-hour IOP profiles would provide additional predictive power beyond these two parameters was not analyzed. Also, the duration of follow-up or any changes in therapy during follow-up were not reported and are potential confounders. It would also have been valuable if the authors reported the relationship between shorter time scale (30-125 minutes or less) fluctuations and glaucoma progression. Nevertheless, the analysis approach and results of this study provide important information about the predictive value of IOP fluctuations at different time scales for progression of glaucoma and the authors are to be congratulated for their work.

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