Correlation and Agreement Between Water Drinking Test and Modified Diurnal Tension Curve in Untreated Glaucoma Patients in Nigeria.

ABSTRACT

PURPOSE: To determine the correlation and agreement between intraocular pressure (IOP) parameters evaluated by the modified diurnal tension curve (mDTC) and the water drinking test (WDT) in primary open-angle glaucoma (POAG) in an indigenous African population. MATERIALS AND METHODS: This was a prospective, interventional, comparative study of 50 newly diagnosed, previously untreated primary open-angle glaucoma patients at the out-patient clinic of the Eleta Eye Institute, Ibadan. A series of IOP measurements were taken 2 hourly (from 700 AM to 300 PM) for the mDTC, using Goldmann applanation tonometer. The WDT was performed thereafter. The patients drank 800 mL of water within 5 minutes, and another series of IOP measurements were taken every 15 minutes for a duration of 1 hour from the moment water was fully ingested. Both the mDTC and the WDT were performed on the same day. IOP peak, mean, and IOP fluctuations were estimated from the data collected. Comparison between the mDTC and the WDT was performed using the paired Student T test for means, Pearson correlation analysis for correlation, and Bland-Altman analysis for agreement. RESULTS: Estimated IOP parameters were significantly higher for the WDT than for the mDTC. The average peak IOP was 27.8±4.0 mm Hg during the WDT and 24.9±3.1 mm Hg during the mDTC (P<0.001). The average mean IOP was 25.8±3.6 mm Hg during the WDT and 22.3±2.4 mm Hg during the mDTC (P<0.001). The average IOP fluctuation was higher (6.6±2.9 mm Hg) during the WDT compared with 4.7±2.0 mm Hg during the mDTC. The mean and peak IOPs were strongly correlated between the mDTC (r=0.729, P<0.001) and the WDT (r=0.658, P<0.001). IOP fluctuation, however, showed weak correlation between the mDTC and the WDT (r=0.258, P=0.709). CONCLUSIONS: There is a strong positive correlation between IOP parameters (peak and mean IOP) estimated from the WDT and the mDTC. The peak and mean IOP can be estimated from the WDT, which is quicker, compared with the mDTC. This is more relevant in low resource settings with limited personnel, time, and resource constraints. In addition, higher IOP values were obtained from the WDT compared with the mDTC, and therefore could serve as a useful practical way to determine target peak in order to optimize IOP control in glaucoma patients.