Blood–aqueous barrier

The blood–aqueous barrier is a selective interface between blood and the aqueous humor that limits and regulates substance movement into the eye’s anterior chamber.

Aqueous humor: A clear fluid that fills the eye’s anterior and posterior chambers and supplies nutrients to avascular tissues. The barrier regulates which substances enter this fluid from blood.
Uveitis: Inflammation of the uvea, the eye’s iris, ciliary body, and choroid. Inflammation can disrupt the barrier and allow proteins and cells into aqueous humor.
Anterior chamber: The fluid-filled space between the cornea and iris. This is the principal chamber whose aqueous contents are protected from blood.
Blood–aqueous barrier breakdown: An increase in barrier permeability that allows normally restricted substances to enter aqueous humor. Its triggers and duration differ across inflammation, surgery, trauma, and systemic disease.
Ciliary epithelium: The epithelial layers of the ciliary body, including the nonpigmented layer that secretes aqueous humor. Tight junctions between nonpigmented cells form a major part of the barrier.
Aqueous flare: Visible light scattering by proteins and other particles in the aqueous humor. Aqueous flare is a clinical sign of increased barrier permeability.
Ciliary body: A ring-shaped eye structure that produces aqueous humor and helps control lens shape. Its epithelial layers form one of the barrier’s two main anatomical sites.
Ocular inflammation: An immune response within eye tissues that can cause pain, redness, and impaired vision. Inflammatory signals alter junctions and transport at the blood–aqueous interface.
Iris vascular endothelium: The endothelial lining of blood vessels within the iris. Its tight junctions restrict passage from iris blood vessels into the aqueous humor.
Fluorescein angiography: An imaging technique that tracks fluorescent dye through blood vessels and ocular tissues. Dye leakage can reveal breakdown of the barrier in the anterior eye.

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