A Comparative Study of the Water Drinking Test in Eyes With Open-Angle Glaucoma and Prior Trabeculectomy or Tube Shunt

Purpose: To compare the intraocular pressure (IOP) response after the water drinking test (WDT) in patients who have undergone trabeculectomy or tube shunt surgery. Methods: This prospective study examined 40 eyes of 34 open-angle glaucoma subjects who had undergone trabeculectomy (n = 20) or tube shunt surgery (n = 20). Both groups were matched by IOP range and by number of topical antiglaucoma medications used. After a baseline IOP assessment, subjects drank 10mL water per kg body weight over 15 minutes. IOP was then measured with a Goldman tonometer every 15 minutes over a 1-hour period. Outcomes measures were IOP peak, fluctuation, mean, and range. Results: No significant differences in baseline demographics, baseline clinical characteristics or IOP changes during the WDT were observed between the 2 surgical procedure groups. Mean baseline IOPs for the tube shunt and trabeculectomy groups were 12.55 +/- 4.23 and 12.3 +/- 4.28mm Hg, respectively (P = 0.854). In the trabeculectomy and tube shunt groups, respectively, peak IOP was 16.25 +/- 5.55 and 16.15 +/- 5.36mm Hg (P = 0.954); IOP fluctuation (IOP max-IOP baseline) was 3.95 +/- 2.17 and 3.6 +/- 2.23mm Hg (P = 0.618), and IOP range was 2.78 +/- 1.56 and 2.8 +/- 1.47mm Hg (P = 0.959). Statistical analysis of IOP fluctuation associations using multivariable linear regression determined that the use of systemic antihypertensive blood pressure medication was associated with an increase in IOP fluctuation of approximately 2mm Hg. Conclusions: Subjects who had undergone either trabeculectomy or tube shunt surgery showed a similar IOP response to the WDT. Subjects on systemic antihypertensive medications experienced significantly greater IOP fluctuations during the test.