1. Functions of tear film  Smooth optical surface at the air-eye interface  Removal of debrise in eye surface  To protect the ocular surface  To supply oxygen, growth factors and other compounds to the corneal epithelium  Contain antimicrobial agents  Lubricates the cornea-eyelid interface

2. Tearfilm is a trilaminar structure  Lipid layer a: retard evaporation b: optical properties c: prevent tear overflow  Aqueaus layer a: consist of electrolytes, water and protein b: secreted by main and accessory glands  Mucin layer a: facilitated distribution of tear film b: stabilizing the tear film c: lubricated globe-eyelid surface

3.  Tear secretion has two components 1- basic secretors 2- reflex secretors  Eyelidmovement is important in tear film renewal, distribution, turnover and drainage  Tear dry function 1- change in the amount of tear film 2- change in the composition of tear film 3- uneven dispersion of the tear film because of corneal-surface irregularities 4- ineffective distribution of tear film caused by eyelid-globe incongruity

4. Tear dysfunction management  Creating a more regular corneal or conjunctival contour  Facilitating eyelid-globe congruitg especially managing of entropion and ectropion  Decreasing evaporation of tear ( room temperature or humidity)  Topical tear substitutes  Reduction of tear drainage (punctal occlusion)  Dressing sunglasses