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James D. Lindsey, Karen Duong-Polk, Robert N. Weinreb; Differences In The Drainage Of 3kDa And 40kDa Tracer From Anterior Chamber Aqueous Humor Revealed By 2-photon Scanning Laser Microscopy. Invest. Ophthalmol. Vis. Sci. 2011;52(14):6615.
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To evaluate the outflow routes of smaller aqueous macromolecules from the anterior chamber, the kinetics of the intraocular distribution of different sized labeled dextrans were compared following intracameral injection.
Anesthetized adult albino (SD) rats received monocular intracameral injection of lysine fixable 3kDa dextran-Cascade Blue or 40kDa dextran-Texas Red. After 5-40 minutes, the eyes were enucleated and immersed in fresh formaldehyde. Whole eyes were examined by 2-photon scanning laser microscopy. Stacks containing 600 images were collected at the limbus spanning from inside the sclera through the depth of the uveal tract. These stacks were assembled into rotating 3-dimensional reconstructions of tracer distribution within tissues near the angle that included Schlemm's canal, iris, and the ciliary body.
During the first 10 minutes after injection, substantial 40kDa dextran remained in the anterior chamber and appeared as a cloud near the anterior angle. A discontinuous tubular structure at the base of the angle likely corresponded to Schlemm's canal. Below this tubular structure, 40kDa dextran appeared as many small clouds throughout the ciliary body that frequently anastomosed into highly branched networks. At 20 and 40 minutes, the amount of anterior chamber 40kDa tracer diminished while the amount in the ciliary body increased. In contrast, by 5 minutes post injection, only occasional small flecks of 3kDa dextran remained in the otherwise clear anterior chamber. However, substantial 3kDa dextran was present inside and adjacent to crenate radial blood vessels in the iris. Relatively straight columns of 3kDa dextran also appeared in ciliary body along side occasional tubules likely to be blood vessels. The intensity of these labeling patterns were markedly diminished by 10 minutes post injection and were largely absent by 20 minutes post injection.
These results confirm that the outflow route of 3kDa macromolecules in aqueous humor differs from 40kDa macromolecules. Moreover, they suggest that 3kDa macromolecules exit in part via iris blood vessels.
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