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L. Wang, G.A. Cull, B. Fortune, G.A. Cioffi; Microspheres Size Optimization in Ocular Blood Flow Measurement in Rats . Invest. Ophthalmol. Vis. Sci. 2006;47(13):470.
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© ARVO (1962-2015); The Authors (2016-present)
Rats are commonly used experimental animals in eye research, however, effective measurement of ocular blood flow remains a problem. Microsphere techniques, which have been successfully used in large animals, become technically and theoretically difficult in rats. Pilot study indicated that the commonly used microsphere sizes and doses from large animals would not work properly in the ocular tissues of rats. The purpose of the study is to optimize the microspheres sizes for the ocular blood flow measurement in rats.
Adult Brown Norway rats were general anesthetized. Blood pressure was maintained between 80 –110 mmHg. Five million fluorescent microspheres of 10, 8 or 6 µm in diameter (in 0.4–0.6 ml suspension) were administered into left ventricle by trans–diaphragm puncture in three groups. Reference blood was drawn from one femoral artery. Retina and choroid were flat–mounted; optic nerve was cryo–sectioned. All microspheres in the tissues and the reference blood were counted semi–automatically and the blood flow per tissue unit was calculated.
The mean arterial pressure during the microspheres injection showed no statistical difference within and between all the groups (One–way ANOVA, P=0.67). The average count of 8 µm microspheres per retina (922±271) was significantly higher than 10 and 6 µm (585±157 and 508±230, respectively, P=0.02, unpaired t–test). For the choroid, the 10 µm microspheres produced the highest number compared to the 8 and 6 µm (8,243±2,244 vs. 5,435±1,917 and 1,466±952 per tissue; P=0.03 and <0.001, respectively). In the optic nerve, the 8 µm microspheres yielded highest number, 9.9±2.8 per mm tissue, compared to 5.7±3.8 and 2.5±0.5 by 10 and 6 µm (P=0.02 and 0.003, respectively). Blood flow rates (µl/min per tissue) measured with 10, 8 and 6 µm microspheres were 11.5±4.5, 19.0±9.0 and 17.0±5.5 for the retina, 170±87, 121±84 and 49±26 for the choroid, respectively. Blood flows in the optic nerve (µl/min/mm) were 0.10±0.06, 0.19±0.04 and 0.04±0.02, respectively.
The ocular blood flow in rats can be reproducibly measured with 8 µm microspheres for the retina and optic nerve, larger than 10 µm for the choroid.
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