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Susan Su, Niranchana Manivannan, Gary Lee, Angelina Covita, Mary K Durbin; Effects of water drinking test on ocular blood flow using optical coherence tomography angiography. Invest. Ophthalmol. Vis. Sci. 2020;61(9):PB00140.
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Increased intraocular pressure (IOP) is a major risk factor for the development of glaucoma and its progression. Literature has proposed the water drinking test (WDT) as a practical method to predict the IOP peak of diurnal tension curve. This preliminary study assesses changes in macular and peripapillary vascular microcirculation using optical coherence tomography angiography (OCTA) metrics after WDT in healthy eyes.
Five healthy subjects (age 37±7.9 years) underwent the WDT, which involved drinking a 1-liter water load in 5 minutes after 4 hours of fasting. IOP using non-contact tonometry and OCTA scans from CIRRUS™ 6000 AngioPlex (ZEISS, Dublin, CA) were obtained at baseline before WDT, 15, 30, 45, and 60 minutes after the water intake. Angio 6 mm x 6 mm and optic nerve head (ONH) Angio 4.5 mm x 4.5 mm cube scans were acquired in the macula and the ONH, respectively. Multi-layer segmentation created en face images of the superficial retinal layer of the macular and peripapillary regions. Macular vessel density (VD) and perfusion density (PD) metrics and ONH PD and flux metrics were provided by the instrument.
Increase in IOP was observed for all subjects with an average increase of 3.72 ± 1.35 mmHg (3 subjects spiked at 30 min, 1 subject at 15 min and 1 subject at 60 min). In the ONH, a slight increase in flux beginning at 30 min (1.85 ± 6.02%), was observed, but it was not statistically significant (Fig. 1) and the flux returned to baseline at 60 min. No appreciable change was observed in ONH PD. In the macula, decreases in VD (-4.98 ± 7.0%) and PD (-4.97 ± 6.1%) were observed beginning at 30 min, but were not statistically significant (Fig. 2). Additionally, any transient effects appeared to have abated by 60 minutes.
The results of this pilot study suggest that healthy subjects exhibit autoregulation of ocular blood flow, as measured by OCTA metrics, following induced changes in IOP. However, the study cohort size was limited and further investigations are warranted with larger and diseased populations.
This is a 2020 Imaging in the Eye Conference abstract.
Figure 1. PD and flux vs. time in the ONH. No appreciable change in ONH PD with IOP changes after WDT. In contrast, an increase in flux was observed though not statistically significant.
Figure 2. VD and PD metrics vs time in the macula. A decrease, though not statistically significant, in superficial macular VD and PD were observed with IOP increase.
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