Читать книгу Essentials of Veterinary Ophthalmology - Kirk N. Gelatt - Страница 87

The BAB depends primarily on the tight junctions in the nonpigmented ciliary body epithelium, the nonfenestrated iris capillaries, and the posterior iris epithelium. The anterior BAB in the iris allows transcellular transport by means of vesicles. Paracellular transport is controlled by tight junction extensions. The anterior surface of the iris does not serve as a barrier as it does not have a continuous cellular layer. The epithelial portion of the BAB is the inner, nonpigmented ciliary epithelium, and it controls the flow of fluid into the posterior chamber. The BAB is less effective than the retinal epithelial barrier, because protein can pass into the AH through leakage in other parts of the anterior uvea. Both the ciliary body and choroidal blood vessels are highly fenestrated and thus leak most of their plasma components, including protein, into the stroma. No barrier is present between the AH and the vitreous humor, which allows the diffusion of solutes from the posterior aqueous into the vitreous humor, or between the anterior uvea and the sclera. Breakdown of the BAB is seen clinically as an “aqueous flare” in anterior uveitis or secondary to loss of AH, as in anterior chamber paracentesis.