Water drinking test induces IOP peaks in POAG, PACG
The investigators subjected 30 PACG or POAG patients (mean age 62.0±7.8 years; 60 percent female), corresponding to 30 eyes, to a comprehensive ophthalmological examination. Evaluations of visual field (VF) were performed 6 months at most before the WDT.
After a 2-hour fast, each participant was made to drink a volume of water that was proportional to their body weight in 10 minutes. Body weight was subsequently measured. IOP measurements were obtained at baseline at every 15 minutes for an hour after the WDT.
Of the 30 participants, 15 were diagnosed with POAG and 15 with PACG. There were no significant differences in average IOP, age and central corneal thickness between the groups. As expected, the axial length (p=0.003) and anterior chamber depth (p<0.001) were significantly lower in the PACG group compared with the POAG group. [Indian J Ophthalmol 2017;64:919-923]
Overall, the mean body weight was 62.1±11.4 kg. The mean volume of water intake was therefore 621.5±114.3 mL per patient.
Mean baseline IOPs for the PACG and POAG groups were 15.55±2.90 and 16.08±2.65 mmHg, respectively (p=0.950).
In the POAG group, there was a significant increase in IOP at 15 minutes (18.64±3.24 mmHg) that persisted until 30 minutes (18.67±3.22 mmHg) after the WDT (p=0.001 for both). In the PACG group, the significant increase was observed at 15 minutes (17.83±4.46 mmHg; p=0.003), 30 minutes (18.36±4.26 mmHg; p=0.001) and persisted until 45 minutes (17.57±3.74 mmHg; p=0.013) after the WDT.
IOP values dropped close to baseline at 45 minutes (17.29±3.68 mmHg) in the POAG group and at 60 minutes (15.65±3.32 mmHg) in the PACG group. The mean peak IOP measurements for the POAG and PACG groups were 19.87±3.44 and 19.14±4.32 mmHg, respectively.
Across all time points, there were no significant differences in the individual IOP measurements and in the mean peak IOP (p=0.771) between the two groups.
The POAG and PACG groups had a mean maximum IOP fluctuation of 23.9 (3.79±1.91 mmHg) and 23.0 (3.61±2.49 mmHg) percent, respectively, from baseline. The difference between groups did not reach statistical significance (p=0.740).
“We found that the two groups displayed very similar IOP curves after water intake, despite differences in ocular anatomy and biometrics,” the investigators noted.
The finding contradicts a previously published study which reports greater fluctuations in IOP in patients with PACG than with POAG after drinking 1 L of water. This discrepancy, however, may be accounted for by population differences, they speculated. “However, considering the high proportion of patients without medications (40 percent) in the open‑angle group in the previous study, we speculate that a large proportion of their participants were glaucoma suspects.”
Anterior chamber depth, axial length, baseline IOP, disease severity and body weight were all unrelated to IOP fluctuations.
Taken together, the findings indicate that “choroidal expansion‑related angle narrowing does not play a major role in IOP increases during WDT.” Instead, factors that are common to both types of glaucoma, such as variations in osmolality, haemodynamics and blood pressure, are more involved in the IOP fluctuations caused by the WDT, the investigators said.