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Editors Selection IGR 9-4

Intraocular Pressure: Peak IOP and water drinking test

Comment by Felipe Medeiros on:

21839 Does peak intraocular pressure measured by water drinking test reflect peak circadian levels? A pilot study, Kumar RS; de Guzman MH; Ong PY et al., Clinical and Experimental Ophthalmology, 2008; 36: 312-315

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Kumar et al. (1086) performed a study to investigate whether the intraocular pressure (IOP) levels obtained during a water-drinking provocative test (WDT) would be related to IOP levels obtained during a diurnal IOP curve. The motivation for their study comes from recent investigations in the literature suggesting that the WDT could be used as a simple test to predict IOP peaks and fluctuations observed during the day. Their study enrolled 25 patients, 16 with primary open-angle glaucoma, seven suspected of having glaucoma based on the appearance of the optic nerve, one with ocular hypertension and one with primary angle-closure glaucoma. Patients with glaucoma were on treatment using different types of medications and two had previous trabeculectomies. The results of the WDT were compared to those from a diurnal IOP curve containing five IOP measurements obtained from 8 am to 5 pm. The authors found a strong correlation between the peak IOP during the WDT and the peak IOP obtained on the diurnal curve (r = 0.876). A poor correlation was found between IOP fluctuations measured by the two methods. Based on their results, the authors suggested that the WDT may provide a satisfactory alternative measure of peak IOP in clinic setting. However, although the authors found a high correlation between the two variables, no analysis of agreement was performed. Two variables may be strongly correlated, but may still show poor agreement. It would be important to see an analysis of the agreement between peak IOP on the WDT and on the diurnal curve, which can be performed using methods such as Bland-Altman plots. It is important to know in how many cases the two measures agreed within clinically acceptable limits, such as 2 mmHg. Without this information, it is not possible to ascertain the real clinical value of the WDT in this situation. It would also be important to evaluate the agreement of WDT IOP peak with peaks of IOP obtained in a 24-hour IOP curve which more appropriately captures the variations of IOP during the day. Further, different types of medications may have different effects on the WDT and it will be important to evaluate the agreement in the different subgroups of patients. However, as the authors recognize, this was a pilot study which will certainly serve to stimulate further research on this important area.

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