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Editors Selection IGR 9-3
Basic Research: Lymphatic vessels in the ciliary body
Comment by James Lindsey on:
24842 Identification of lymphatics in the ciliary body of the human eye: a novel "uveolymphatic" outflow pathway, Yücel YH; Johnston MG; Ly T et al., Experimental Eye Research, 2009; 89: 810-819
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.
References
- Bill A. The drainage of albumin from the uvea. Exp Eye Res 1964; 3: 179-187.
- Field EJ, Brierley JB. The retro-orbital tissues as a site of outflow of cerebrospinal fluid. Proc R Soc Med 1949; 42: 447-450.
- Patek PR, Bernick S. Extravascular pathways of the eye and orbit. Am J Ophthalmol 1960; 49: 135-141.
- Krebs W, Krebs IP. Ultrastructural evidence for lymphatic capillaries in the primate choroid. Arch Ophthalmol 1988; 106: 1615-1616.
- Sugita A, Inokuchi T. Lymphatic sinus-like structures in choroid. Jpn J Ophthalmol 1992; 36: 436-442.
- Schroedl F, Brehmer A, Neuhuber WL, Kruse FE, May CA, Cursiefen C. The normal human choroid is endowed with a significant number of lymphatic vessel endothelial hyaluronate receptor 1 (LYVE-1)-positive macrophages. Invest Ophthalmol Vis Sci 2008; 49: 5222-5229.
- Birke K, Lütjen-Drecoll E, Kerjaschki D, Birke MT. Expression of podoplanin and other lymphatic markers in the human anterior eye segment. Invest Ophthalmol Vis Sci 2010; 51: 344-354.
- Camelo S, Kezic J, Shanley A, Rigby P, McMenamin PG. Antigen from the anterior chamber of the eye travels in a soluble form to secondary lymphoid organs via lymphatic and vascular routes. Invest Ophthalmol Vis Sci 2006; 47: 1039-1046.
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