The eye is a direct extension of the CNS. The clarity of its different structures and media and its exposure outside the body create ideal conditions for local delivery of drugs. In appearance, the eye seems easily accessible but delivering drugs to the eye remains one of the major challenges of modern ophthalmology. The ocular surface forms a complex association of secreted fluid layers with the cornea to protect the eye from outside aggression. Besides high resistance of the tight-junction corneal epithelium, the structure of the cornea formed by a succession of lipidic and hydrophilic layers itself limits transcorneal penetration of compounds. The eye, similar to the brain, is protected from the systemic circulation by tissue and cell barriers: the tight-junction of the ciliary body epithelium; the retinal pigment epithelium and endothelial cells of the iris; and the retina. Therefore, anatomic and dynamic barriers for drug penetration into the eye tissues exist.
展开▼
