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An important question for understanding aqueous outflow is how uveoscleral outflow exits the eye. It has been known that labeled albumin injected into the suprachoroidal space will appear in extraocular lymphatic vessels and several associated lymph nodes.1 Yet whether there are lymphatic vessels inside the eye that could be involved in uveoscleral outflow has remained con troversial.2-7
Addressing this issue, Yücel et al. (1388) identified vessel-like structures in the ciliary muscle that were immunoreactive for lymphatic vessel markers but not immunoreactive for blood vessel markers. Overall, the techniques were appropriately controlled, and generally well described. However, the magnification of the electron micrographs was too low to see the immuno-gold label. Use of a highly sensitive tyramide signal amplification technique may explain why they were able to see these vessel-like structures whereas similar studies using conventional detection methods did not detect vessel-like structures.6,7
Prior studies have demonstrated transport of macromolecules from the anterior chamber to lymph nodes in the neck.1,8 Prior studies also have presented important evidence for intraocular lymphatic vessels.4,5 Though their demonstration of beads inside of Lyve-1 positive channels does suggest active lymphatic vessel uptake within in the ciliary body, further studies will be needed to confirm that these channels represent lymphatic vessels that extend to head and neck lymph nodes. If this is true, additional studies will be needed to show whether these vessels can transport significant amounts of aqueous humor. Nevertheless, this study provides important new support for the idea that lymphatic vessels in the ciliary body contribute to uveoscleral outflow.