Schlemm's canal: more than meets the eye, lymphatics in disguise.

Schlemm's canal (SC) is a unique vascular structure that functions to maintain fluid homeostasis by draining aqueous humor from the eye into the systemic circulation. The endothelium lining the inner wall of SC has both blood and lymphatic vascular characteristics, thus prompting exploration of the development and regulation of this unique channel. In this issue of the JCI, back-to-back papers by Aspelund et al. and Park et al. detail the mechanisms of SC development, which includes a lymphatic reprogramming that is necessary to maintain proper function. Furthermore, both groups exploit the lymph-like qualities of this canal: they identify VEGF-C as a potential therapeutic for glaucoma and suggest that expression of PROX1, a marker of lymphatic fate, could also serve as a biosensor for monitoring SC integrity. These studies provide substantial insight into the molecular and cellular pathways that govern SC development and reveal that ocular pathology is associated with deregulation of the lymph-like characteristics of SC.