The effect of the water-drinking test on aqueous humor dynamics in healthy volunteers

In 19 healthy volunteers (9 men, 10 women) we studied the effect of drinking 1000 ml of water within 10 min on aqueous humor dynamics. Fluorescein was applied topically five times, 6 h before measurements. All readings were taken during the afternoon. The Wilcoxon signed-rank test was used to evaluate the statistical relevance of the data. Aqueous humor flow was measured 60 min before (F1) and 10 min (F2), 30 min (F3), 60 min (F4) and 90 min (F5) after drinking 11 of water. Flow (mean ± SD) changed as follows: F1, 2.25 ± 1.2 ll/min ; F2, –3.29 ± 3.4 /min (P < 0.0000); F3, 1.69 ± 1.0 gml/min (P=0.007); F4, 2.39±0.9 l/min (P=0.25); F5, 2.64±0.9 l/min (P=0.02). Three to four days later the identical procedure was performed in each individual: F1, 2.06 ± 1.0 l/min F2, –3.12 ± 2.4 l/min (P < 0.0000); F3, 1.09 ± 0.6 l/min (P < 0.0001); F4, 1.76 ± 0.6 l/min (P=0.15); F5, 2.54±0.8 l/min (P=0.01). The correlation coefficient for the left and night eyes (F1–F5, both days) was r=0.85. The mean flow in the 19 healthy volunteers during the afternoon hours was 2.25 ± 1.0 l/min. Water load consistently led to a reflux of unbound fluorescein into the eye about 10 min later. This is documented as a negative flow. Ninety minutes after drinking 1000 ml of water there is a significant increase in flow, which is in contrast to the normal diurnal curve of aqueous humor dynamics. Water load causes hydremia and an increase in episcleral venous pressure. Fluorophotometry together with water load may be useful to study the aqueous humor dynamics in healthy and glaucomatous eyes and eyes with ocular hypertension.