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Editors Selection IGR 18-4

Clinical Examination Methods: Diurnal IOP Patterns in Healthy Subjects

Comment by Tony Realini on:

72758 Long-term Reliability of Diurnal Intraocular Pressure Patterns in Healthy Asians, Chun YS; Park IK; Shin KU et al., Korean Journal of Ophthalmology, 2017; 31: 132-137

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Chun and colleagues have recently reported a study evaluating the re-peatability of diurnal intraocular pressure (IOP) patterns in heathy Asian subjects without glaucoma. In this study, IOP was measured using Goldmann applanation tonometry every 2 hours from 9AM to 11PM on two days separated by 8 weeks. At each visit, IOP mean, peak, trough and fluctuation (assessed both as peak minus trough and as standard deviation of all measurements). Using the intraclass correlation coefficient as a measure of agreement, the investigators found excellent agreement of diurnal summary parameters and IOP at individual time points between these two sessions. They concluded, "These findings suggest that IOP measurements at standardized times of the day will be useful for assessing the effectiveness of glaucoma therapy." As our group and others have demonstrated, the significant spontaneous variability of IOP over time can confound the accurate assessment of therapeutic efficacy in glaucoma management. I applaud the authors for their carefully designed and analyzed study addressing this important topic. I caution readers, however, to consider whether some elements of the study design and the data themselves may weaken support for the stated conclusions of the analysis. The study was conducted in healthy subjects without glaucoma. Assuming that IOP regulation in healthy and glaucomatous eyes is comparable is problematic. The trabecular meshwork (TM) is integral to IOP regulation, and in contrast to the presumed healthy TM in the subjects in this study, patients with glaucoma are known to have trabecular dysfunction that likely alters IOP regulation in glaucomatous eyes. More importantly, this study was conducted in Asian eyes, known to have very low IOP levels. In this study, the mean IOP was 12.2 mmHg at each visit, and peak and trough values averaged only 1 mmHg above or below the mean, respectively, yielding IOP fluctuations on the order of 2-3 mmHg by the peak minus trough method and only 1 mmHg using the standard deviation method. Such minimal fluctuations bias toward higher agreement: if values don't change much, they will agree by default. It remains my belief that assessment of therapeutic efficacy of glaucoma treatment should be based on the difference between several pre-treatment IOP measurements and several on-treatment IOP measurements, to better distinguish the signal from the noise.

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