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Editors Selection IGR 16-4

Basic Research: 24hr Applanation vs. Perkins TM

Comment by Tony Realini on:

26606 Untreated 24-h intraocular pressures measured with Goldmann applanation tonometry vs nighttime supine pressures with Perkins applanation tonometry, Quaranta L; Konstas AGP; Rossetti L et al., Eye, 2010; 24: 1252-1258

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Quaranta et al. (1136) have conducted an intriguing study in which 100 ocular hypertensive or glaucomatous patients, following washout of all IOP-lowering drugs, underwent 24-hr IOP assessment. IOP was measured every four hours in the sitting position using Goldmann tonometry and in the supine position using Perkins tonometry. They point out that recent data suggesting IOP is highest at night in the supine position has generally been collected using pneumatonometry rather than the clinical standard Goldmann tonometry. Because the Goldmann tonometer cannot be adapted for supine measurement, they utilized Perkins tonometry as a reasonable substitute for supine measurements. They found that supine Perkins measurements were generally higher than same-time sitting Goldmann measurements. The majority of patients exhibited peak sitting Goldmann IOP during daytime hours. Interestingly, mean daytime sitting Goldmann IOP was not statistically different from mean nighttime supine Perkins IOP in this cohort. For approximately 70% of patients, peak daytime sitting Goldmann IOP was within 1 mmHg of peak nighttime supine Perkins IOP. In the context of recently published studies, this new data are perplexing.

Not only are we uncertain about the optimal number and timing of IOP measurements necessary to characterize circadian IOP - we may also have to accept uncertainty about the optimal tonometer choice for the task

Is IOP higher at night when we are supine than during the day when we are upright? Might the pneumatonometer overestimate IOP in the supine position? Or might the Perkins underestimate supine IOP? This study clearly demonstrates the inherent weakness of characterizing a dynamic parameter such as IOP. Not only are we uncertain about the optimal number and timing of IOP measurements necessary to characterize circadian IOP ‐ we may also have to accept uncertainty about the optimal tonometer choice for the task.

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