Purpose:
1) To measure potential change in choroidal thickness (CT) as a cause of intraocular pressure (IOP) rise during the water-drinking test (WDT); 2) To compare WDT responses in persons with open angle glaucoma (OAG), OAG suspects (OAGS), angle closure (AC), AC suspects (ACS) and AC glaucoma (ACG).
Methods:
Spectral domain optical coherence tomography scans of the macula with enhanced depth imaging were obtained (one eye per subject) before and 30 minutes after drinking 1 liter of water, in 25 ACS/AC/ACG and 48 OAGS/OAG subjects. Standard demographics, degree of field loss, and blood pressure were measured (before and after WDT). Average CT (6 mm scan centered on fovea) was measured with Image J software, and univariable and multivariable statistics were performed.
Results:
Baseline CT was thicker in ACG than OAG eyes (312 vs. 244µm, p=0.03). However, CT has been shown to be inversely related to axial length (AL), and OAG eyes had longer AL than ACG eyes (24.3 vs. 23.0 mm, p<0.0001), possibly accounting for this difference. After WD, mean IOP rose 40% (5.51 + 3.51 mm, p<0.0001), and systolic, mean and diastolic blood pressures (BP) also rose (8.9, 6.4, and 5.1 mm Hg, respectively, all p<0.0001), as did systolic perfusion pressure (PP, 3.4 mm Hg, p=0.01). The AL also increased (0.012 mm, p=<0.0001), though the increase was not significantly different between OA and AC eyes (0.009 mm vs. 0.017 mm, p=0.19). The observed increase in AL, most likely associated with an increase in eye volume caused by the increase in IOP, matched the expected increase in AL calculated using the pressure-volume relationship for the eye described previously (Silver and Geyer, Curr Eye Res 2000). Mean CT increased, but insignificantly (1.4 + 16.3 µm, p=0.46). Overall IOP change was not significantly associated with CT change (p=0.8). CT change was unrelated to age, sex, gender, axial length, visual field defect level, baseline IOP or baseline CT. In multivariable models in 64 eyes with >2 mm IOP rise, CT change was significantly related to change in mean or diastolic PP (p=0.02, 0.01), and AC eyes had greater change in CT than OA eyes (p=0.03).
Conclusions:
CT is responsive to PP, yet IOP increase in WDT is associated with BP rise but not with CT increase, suggesting it results from changed aqueous in/outflow related to adrenergic stimulation. Our results confirm thicker choroid in AC eyes and differences in CT reactivity in AC versus OA eyes.