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Ophthalmic DD: Introduction
Anatomy & physiology
Nasolacrimal system
• The surfaces of the cornea and conjunctiva are covered by a film of
tears produced, distributed and excreted by the nasolacrimal system.
• It plays a major role in protecting and hydrating and protecting the eye
surface. It also has significant impact on the amount of drug
absorbed to the eye from topical administration.
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Ophthalmic DD: Introduction
Anatomy & physiology
Nasolacrimal system: tear/lacrimal fluid
Tear fluid composition
• It comprises three layers: a mucous layer adhering to the epithelium ,
an aqueous layer and a superficial lipid layer.
• The mucous layer: may hinder drug delivery by forming a diffusional
barrier to macromolecules, but it may also bind other substances
(mucoadhesive) and prolong residence on the surface of the eye.
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Salma E. EL-Habashy
