Blood-Ocular Barriers

There are two main blood-ocular barriers, the blood-aqueous barrier and the blood-retinal barrier. The blood-aqueous barrier is formed by the nonpigmented ciliary epithelium of the ciliary body and the vascular endothelium of the iris vessels. The blood-retinal barrier is formed by the vascular endothelium of the retinal vessels and the retinal pigment epithelium. Four methods of examination are currently used to study the function of blood-ocular barriers. Among these, laser flare-cell photometry is a noninvasive, quantitative method to evaluate the permeability of the blood-aqueous barrier. Vitreous fluorophotometry is an excellent technique to quantitate blood-retinal barrier function. Fluorescein angiography and optical coherence tomography are excellent qualitative imaging techniques to evaluate blood-retinal barrier function. Current basic research shows prostaglandin E2 and other mediators may produce breakdown of the blood-aqueous barrier, and vascular endothelial growth factor plays an important role in the breakdown of the blood-retinal barrier. Retinal laser photocoagulation can induce breakdown of both the blood-aqueous and blood-retinal barriers in pigmented rabbits. The four methods of examination described herein are excellent measures for clinical application to evaluate blood-ocular barrier function in various ocular diseases, many of which are discussed here. [Tzu Chi Med J 2008;20(1):25–34]