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M. Kim, S. Moore, N. Gupta, Y. H. Yucel, M. Johnston; Measuring Lymphatic Drainage of Aqueous Humor From the Eye: A Sheep Model. Invest. Ophthalmol. Vis. Sci. 2010;51(13):3236.
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We have recently described lymph channels in the human and sheep ciliary body (Yucel et al, Exp. Eye Res. 2009) suggesting a role for lymphatics in aqueous outflow. The purpose of this study was to develop a model to quantify lymphatic drainage from the eye into the lymphatic circulatory system.
Under general anesthesia, right and left cervical lymphatic vessels of sheep (n=3) were cannulated. Intracameral injection of radioactive tracer was performed using 125I - bovine serum albumin (27.9 µg/ in 50 µL saline) for both eyes. Serial samples of lymph from both cervical lymphatics were collected at 15 minute intervals over a period of 3 hours. A catheter placed in a femoral vein for sampling was used to obtain serial blood samples at the same time points. Plasma and lymph samples were assessed in a gamma counter to measure radiation tracer levels. The mean radiation tracer levels and standard deviations were calculated at various time points.
Both cervical lymphatic vessels in each sheep flowed continuously for the duration of the experiment. The average flow rates were 0.047 ± 0.02 mL/min and 0.041± 0.01 mL/min for the right and left cervical lymphatic vessels respectively. Within 15 minutes of intracameral injection, tracer was detected in both lymph and blood collections. Over the next few hours, tracer concentrations continued to increase and at 3 hours, the average concentration of the tracer was 94,160 ± 42,481 cpm/ml in blood, 21,485 ± 5,749 cpm/ml in right cervical and 50,366 ± 34,023 cpm/ml in the left cervical lymphatic vessel.
These findings indicate that lymphatic drainage from the eye does occur, and can be measured continuously in sheep. Further studies are needed to determine the extent and time course of lymphatic outflow from the eye in health and disease.
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