To study the differential effects of various filtering surgeries (Tube and Trabeculectomy) on Intraocular Pressure (IOP) changes after Water Drinking Test (WDT).

In this prospective non-randomized comparative clinical study, WDT was performed in 30 patients who had tube surgery and 30 age- and sex-matched trabeculectomy patients. Only one eye of each patient was included. The IOP at baseline was less than 21 mm Hg in all enrolled eyes with or without adjunctive topical medications. After WDT, the IOP was measured and recorded at 15, 30, 45, and 60 minutes. Then, WDT-IOP results were compared between the two groups.

IOP significantly increased from baseline at all measured time-points after WDT in both groups (P<0.001). In Trab Group, the average IOP increased from 14.8±2.9 mmHg at baseline up to 30 minutes after WDT (18.8±4.7), but decreased afterwards (18.0±5.2 at 60 minutes). In contrast, in the Tube Group, IOP showed increments until the last measurement at 60 minutes (14.2±3.9, 18.8±5.6, and 19.7±6.0 at baseline, 30 and 60 minutes, respectively). The End-Pressure Difference (IOP at 60 minutes vs. baseline) was significantly greater in the tube (5.6±3.6; 41% change) than trabeculectomy group (3.2±4.7; 23% change; P=0.033).

IOP significantly increased after WDT in both tube and trabeculectomy groups. However, IOP starts to decline at 30 minutes after WDT in the trabeculectomy, while it continued to increase up to 60 minutes after WDT in the tube group. This finding may have implications regarding the efficacy or safety of procedures in advanced glaucoma patients.