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M. Shahidi, M. Mori, N. P. Blair, J. Wanek; Retinal Intravascular Oxygen Tension Response to Light Flicker in Experimental Diabetes. Invest. Ophthalmol. Vis. Sci. 2008;49(13):4254.
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. Oxygen delivery is affected by the level of retinal metabolic activity. Light flicker increases the retinal metabolic demand and thus can suitably serve as a means to probe retinal oxygen dynamics in health and disease. We determined the presence of changes in retinal arterial and venous oxygen tension response to light flicker stimulation due to experimental diabetes.
. A laser beam was projected at an oblique angle on the retina following intravenous injection of an oxygen sensitive molecular probe to generate an optical section phosphorescence image in the YZ plane of the retina. Oxygen tension in retinal vasculatures was measured based on phosphorescence lifetime, determined using a frequency-domain approach. For visual stimulation, the illumination light from the slitlamp biomicroscope was flickered at a frequency of 10 Hz. A filter was placed in the path of the illumination to spectrally separate the light flicker stimulus from laser illumination. Optical section phosphorescence imaging was performed prior to initiating and during light flicker. The systemic arterial oxygen tension, blood pressure, and heart rate were measured by cannulation of the femoral artery during imaging. Retinal intravascular oxygen tension measurements were performed in normal control rats and 4 weeks after induction of experimental diabetes by intravenous injection of streptozotocin.
. In normal rats, the average oxygen tension in retinal arteries and veins were 51 + 5 and 29 + 3 mm Hg (before flicker) and 55 + 7 and 29 + 3 mm Hg (during flicker), respectively. The retinal arteriovenous (A-V) oxygen tension difference before and during light flicker were 22 + 3 and 26 + 5 mm Hg, respectively. A significant increase in the retinal A-V oxygen tension due to visual stimulation by light flicker was observed in normal rats (P = 0.004; N = 9). In diabetic rats, the average oxygen tension in the retinal arteries and veins were 47 + 5 and 31 + 4 mm Hg (before flicker) and 46 + 8 and 30 + 4 mm Hg (after flicker), respectively. Retinal A-V oxygen tension before flicker (16 + 6 mm Hg) was similar to measurements obtained during light flicker (16 + 9 mm Hg) (P = 0.92; N = 7). During light flicker, retinal arterial and A-V oxygen tension were significantly reduced in diabetic rats as compared to normal controls (P < 0.03).
. These findings of differences in retinal vascular oxygenation response to increased metabolic demand suggest a disparity between oxygen supply and consumption due to diabetes.
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