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Tong Boon Tang, Mehwish Bhatti, Augustinus Laude; Effects of Water Drinking Test on Blood Flow in Optic Nerve Head using LSFG. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):2743.
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© ARVO (1962-2015); The Authors (2016-present)
Water drinking test (WDT) has been proposed, because of its simplicity, as a potential diagnostic test for glaucoma based on the considerable effect on intraocular pressure (IOP), which is an important risk factor. Also, it has been established that optic nerve blood flow is a risk factor in glaucoma, and literature suggests a reduced ocular blood flow in glaucoma patients. Therefore, optic nerve head (ONH) blood flow monitoring is of high importance in glaucoma. This calls for another investigation if WDT has any effect on ONH blood flow, despite the autoregulation phenomenon.
Laser Speckle Flowgraphy (LSFG) is a non-invasive modality which calculates mean blur rate (MBR) of ocular blood flow, and provides insight on pulse waveform of heartbeat. Various pulse waveform parameters, such as skew, blowout score (BOS), and blowout time (BOT) in the ONH can be estimated. Our experiment involved 5 healthy subjects, who were asked to refrain from eating, drinking, or smoking since two hours before the experiment begins. The subjects were seated in a comfortable experiment room with room temperature being regulated at 25 °C. Initial LSFG reading was taken as a baseline, then the subjects were asked to drink 1 liter of water. LSFG readings were recorded at 5, 10, 15, 20, 25, 30, 40, 50, 60 minutes after the water intake. MBR of ONH, skew, BOT and BOS were examined for all the subjects.
Five subjects participated in the experiment, and their measurements were normalized. The averaged result of heartbeat using error bars with standard deviations was plotted as shown in Figure 1. The results show a slight reduction, although not found to be statistically significant, in all pulse waveforms parameters examined during analysis.
The results showed that healthy subjects exhibited autoregulation of blood flow. Admittedly the sample size is limited, we believe our results may provide important baseline for comparison with glaucoma patients, where a disrupted blood flow causes autoregulation dysfunction in ONH.
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