10) In all avian species, the necessity of blinking is diminished because of the ability of the third eyelid to spread the precorneal
tear film adequately across the cornea.
The ocular surface is normally protected from microbial invasion through an intricate biochemical and anatomic relationship between the cornea, conjunctiva, lacrimal secretory apparatus and precorneal
tear film, and the eye lids.
tear film stability was assessed by measuring the tear film break-up time by scanning the precorneal
tear film with a biomicroscope (Topcon SL1E; Topcon, Tokyo, Japan).
Poor bioavailability of drugs from ocular dosage forms is mainly due to the precorneal
loss factors which include tear dynamics, non-productive absorption, transient residence time in the cul-de-sac, and the relative impermeability of the corneal epithelial membrane.
Examination OS revealed normal upper, lower, and third eyelids; marked conjunctival and episcleral hyperemia; adequate precorneal
tear film; and a clear cornea.