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LG Carnahan, B Khoobehi; Dynamics of Leukocytes and Measurement of Choroidal Hemodynamic Parameters Using Leukocytes Stained with Deeper Infrared Dye . Invest. Ophthalmol. Vis. Sci. 2002;43(13):4354.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To provide a method to measure hemodynamic parameters such as leukocyte speed and volumetric blood flow of the choroid using a deeper infrared dye to better penetrate the tissue. Methods: To isolate the choroid from the retina, retinal ischemia was induced in one eye each of 12 rats. Retina ischemia was performed by closing central retinal veins and arteries with an IR laser at 810 nm (laser parameters: power 300 mW, exposure time 500 ms, and spot size 500 µm). Ten days following the retina ischemic procedure, in vivo staining of leukocytes was performed using the infrared dye perchlorate, which absorbs at 820 nm and fluoresces at 880 nm. In each experiment, 0.1 ml (1 mg/ml) of the dye was perfused through the tail vein in 1 minute. Results: Movement of each individual leukocyte was clearly visible in the choroid of the retinal ischemic eye, as well as in the retina and choroid of the normal eye. At first, only a few leukocytes were seen to fluoresce; however, by 10-15 minutes after the injection, a sufficient number of fluorescent leukocytes were present to allow measurement of hemodynamic parameters. The number of fluorescent leukocytes peaked at 20-30 minutes post injection. With a single injection, the fluorescent leukocyte population was large enough to measure hemodynamic parameters for up to 24 hours. The freeze frame technique, reported in earlier studies, was employed to measure volumetric blood flow of the choroid in the retinal ischemic eye as well as the combined volumetric blood flow of the retina and choroid in the normal eye. Preliminary measurements show volumetric blood flow in the choroid to be 408 ± 25 nl/sec (N=4 animals). Conclusion: Volumetric choroidal blood flow was measured for the first time using the cell labeling technique. This hemodynamic parameter was measured in the isolated choroid in eyes with induced retinal ischemia. However, this technique can also be used without isolating the choroid by subtracting the volumetric blood flow in the retina obtained with the visible dye, which allows the stained cells circulating only in the retina to be imaged and removed from the combined retina and choroid image.
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