الفهرس 
Patient and methodsOnly 14 pages are availabe for public view
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Abstract
The human tear film coats the anterior surface of the eye and is composed of three distinct layers: an inner mucin coating, a middle aqueous component, and a lipid overlay. Traditionally, the mucin layer was felt to be derived from goblet cells of the conjunctiva, the aqueous component from the lacrimal gland, and the lipid layer from the meibomian glands. (8) Recent advancements in proteomics have slightly altered this view of the tear film by identifying mucin as a product of the goblet cells but the lacrimal gland as well. The 3-layered tear film inhibits ocular surface invasion by pathogens, provides an air-tissue interface for gas exchange, and supplies essential nutrients and metabolites to maintain a transparent and avascular cornea. (8) I.1. Embryology of lacrimal system The orbital walls are embryologically derived from neural crest cells. Ossification of the orbital walls is completed by birth except at the orbital apex. The lesser wing of the sphenoid is initially cartilaginous, unlike the greater wing of the sphenoid and other orbital bones that develop via intramembranous ossification. The membranous bones surrounding the lacrimal excretory system are well developed at 4 months of embryologic age and ossify by birth. (9) The lacrimal gland begins development at the 22 to 25 mm embryologic stage as solid epithelial buds arise from the ectoderm of the superolateral conjunctival fornix. Mesenchymal condensation around these buds forms the secretory lacrimal gland. The early epithelial buds form the orbital lobe in the first 2 months, whereas the secondary buds.