title: Understanding the mechanism of the water drinking test: the role of fluid challenge volume in patients with medically controlled primary open angle glaucoma.
abstract: BACKGROUND
  To determine whether a 500-mL fluid challenge produces a different intraocular pressure (IOP) response profile compared with a 1000-mL water drinking test (WDT).
  
  
  METHODS
  Prospective, observer-masked, cross-over, observational study. Patients with primary open angle glaucoma were recruited from a private specialist glaucoma practice. One eye of each patient was included. Subjects were randomized to receive either a 500-mL or 1000-mL fluid challenge. Baseline IOP was recorded with a Goldmann applanation tonometer and then every 15 min for 1 h. A second WDT with the alternate volume of water was performed after a minimum washout period of 24 h. Primary statistical analysis was performed using a two-way anova repeated measures of variance with a Bonferroni post-hoc test.
  
  
  RESULTS
  Fifteen patients were included in this study. The mean patient age was 67.0 +/- 10.2 (SD) years, and 60% of patients were female. There was no statistically significant difference in baseline IOP between the 500-mL and 1000-mL WDTs (P = 0.11). Both fluid challenge volumes produced a statistically significant rise in IOP from baseline at 15, 30 and 45 min after water ingestion. However the mean maximum increase in IOP was less in the 500-mL WDT (3.3 +/- 1.8 mmHg [23.9%]) compared with the 1000-mL WDT (4.9 +/- 2.3 mmHg [32.5%]; P = 0.0095).
  
  
  CONCLUSIONS
  The 500-mL WDT may provide an alternative for patients who are unable to tolerate drinking 1000 mL of water. However, because the maximum IOP obtained is less, a 500-mL WDT cannot be used to directly estimate peak diurnal pressure.
authors.affiliation: Department of Ophthalmology, University of Auckland, New Zealand.
authors.forename: Nathan M
authors.initials: NM
authors.lastname: Kerr
authors.forename: Helen V
authors.initials: HV
authors.lastname: Danesh-Meyer
mesh_terms: D000368:Aged; D002940:Circadian Rhythm; D018592:Cross-Over Studies; D004326:Drinking / Q000502:physiology*; D005260:Female; D005902:Glaucoma, Open-Angle / Q000503:physiopathology*; D006801:Humans; D007429:Intraocular Pressure / Q000502:physiology*; D008297:Male; D011446:Prospective Studies; D014065:Tonometry, Ocular; D014792:Visual Acuity; D058609:Visual Field Tests; D014867:Water / Q000008:administration & dosage*
chemical_list: D014867:Water