Hematic and fluid barriers in the optic nerve

Hematic and fluid barriers in the optic nerve have been studied by tracing the in vivo penetration of diaminoacridines in tissue nuclei and tissue fluids. Diaminoacridines were administered at non‐toxic doses and were detected by the fluorescence they produced when properly excited. Diaminoacridine concentrations of 10−6M or higher in circulating blood failed to penetrate into tissues and fluids protected by hemato‐encephalic or hemato‐ocular barriers. However, fluoresence was found in: (a) optic nerve dura mater including the mesothelium lining its inner surface, but not in the subjacent arachnoid, pia, or cerebrospinal fluid; (b) all orbital and dural vessel walls, including their endothelium, but not in the pial nor optic nerve vessel walls; (c) choroid, sclera, and Kuhnt's tissue, but not in the optic nerve. Diaminoacridine concentrations of 10−6M in cerebrospinal fluid produced fluorescence in optic nerve tissues and vessels, including their endothelium, and meninges, including dural mesothelium, but not in retina or vitreous. Similar concentrations in the vitreous showed fluorescence in the retina and optic nerve head tissues, but not farther in the optic nerve. Thus: (a) there is a blood‐optic nerve barrier; (b) this barrier is located in the mesothelium lining the inner dural surface, in pial and optic nerve vessels endothelium, and Kuhnt's tissue; (c) endothelium and mesothelium showed one‐way permeability; (d) there is a vitreous optic‐nerve barrier preventing passage of fluids from optic nerve to vitreous or vice versa.