Evidence of lymphatics in the rat eye retina.

Background: The lymphatic structure of the eye is still under debate. It is mainly assumed that the retina is primarily drained by prelymphatics and not by lymphatics per se. We aimed to identify lymphatics in the rat retina.

Methods: Eyes from ten Wistar rats were paraffin-embedded and the lymphatic marker podoplanin (D2-40) was investigated.

Results: We identified in the rat retina a blunt-end network of lymphatic endothelial vessels. It consisted of circumferential vessels within the outer and, respectively, inner plexiform layers, connected by radial dichotomous vessels. Moreover, D2-40 expression was found within the choroid, ciliary body, and extraocular muscles.

Conclusions: This in situ evidence is strongly supported by the recent in vitro demonstration of the expression of lymphatic markers in retinal endothelial cells. Further studies of comparative histology should use specific lymphatic markers to test whether other species besides rats have proper retinal lymphatics.