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Editors Selection IGR 24-3
Clinical Examination Methods: Diurnal IOP Patterns in POAG and PACG
Comment by Andrew Tatham on:
73244 Association of Glaucoma-Related, Optical Coherence Tomography-Measured Macular Damage With Vision-Related Quality of Life, Prager AJ; Hood DC; Liebmann JM et al., JAMA ophthalmology, 2017; 135: 783-788
It is well established that intraocular pressure (IOP) fluctuates, with sleep laboratory studies showing peak IOP often occurs during the nocturnal period.1 The ability to obtain a greater number of IOP measurements, including outside office hours, is likely to improve understanding of the role of IOP as the major risk factor for glaucoma, and improve ability to determine the efficacy of IOP-lowering treatments.
Tan and colleagues taught 31 patients with primary angle closure glaucoma (PACG) and 22 with primary open angle glaucoma (POAG) to perform self-tonometry using the iCare ONE rebound tonometer (RBT) (iCare Finland, Oy, Finland). This device uses a probe which makes 6 rapid con-secutive contacts with the central cornea and records the mean measurement as the IOP. Patients measured their own IOP in the sitting position 5 times per day at 4 hourly intervals from 8am to midnight for 7 days. At least 3 successful measurements were required at each time point and the mean IOP at each time point over the 7 days was calculated for each subject to provide an individual's 'diurnal IOP profile'.
Overall IOP was highest at 8 am and tended to drop during the day to reach a low at midnight, with similar patterns of IOP fluctuation seen in eyes with PACG and POAG. IOP was significantly higher at 8am compared to 8pm and midnight for both groups; however, the range of IOP fluctuation was modest with a median range of 2.3mmHg in eyes with PACG and 3.2 mmHg in POAG. It is, however, important to emphasize that patients were medically treated and eyes with PACG had received prior laser iridotomies; one would expect IOP fluctuation may be greater in untreated patients. There were other subtle differences between groups: eyes with POAG were noted to have slightly greater IOP fluctuation and eyes with PACG had higher trough IOP. However, there was no significant difference in average or peak IOP between groups. The RBT showed good agreement with Gold-mann applanation tonometry with a mean underestimation of only 0.15 ± 0.65 mmHg.
The differences between POAG and PACG may have been due variation in number and type of medication or differences in the effect of dilation status on IOP. An interesting finding was that eyes with POAG tended to have higher IOP during the day but at midnight IOP was significantly higher in eyes with PACG. The authors hypothesize that this may be due to nocturnal pupil dilation causing impaired aqueous humour outflow at night in PACG. Although the significance of IOP fluctuation for glaucoma progression is yet to be determined, this study supports others in showing self-tonometry is feasible and can be used to improve understanding of IOP fluctuations in patients' ambient environment.2 A limitation is that although RBT allows a great number of IOP measurements, it does not record IOP continuously. Only 5 measurements were taken each day and no measurements were taken between midnight and 8 am, meaning the true timing of peak IOP and magnitude of fluctuation remains uncertain. Nevertheless, the days of ophthalmologists relying on single IOP measurements to set treatment targets and assess response to treatment may be near an end.
References
- Liu JH, Zhang X, Kripke DF, Weinreb RN. Twenty-four-hour intraocular pressure pattern associated with early glaucomatous changes. Invest Ophthalmol Vis Sci. 2003;44(4):1586-1590.
- Pronin S, Brown L, Megaw R, Tatham AJ. Measurement of intraocular pressure by patients with glau-coma. JAMA Ophthalmology 2017; 135(10):1030-1036.
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