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This is the view of the cornea and lower limbus of an eye that has a drop of fluorescein placed.

1.	This study demonstrates:
	e -- all of the above Fluorescein dye is used to stain the tear film layer. The tear film covers the normal ocular surface. The tear film, stained green with fluorescein, is on the corneal epithelium. The air-tear film interface is the initial and most important refractive surface of the eye. Maintenance of a stable, healthy tear film, based on the neuro-anatomic integration of cranial nerves V and VII is necessary for normal vision. Disruption of this neuro-anatomic integration at any location will result in an unstable tear film, decreased vision, and disruption of the ocular surface.
2.	A unique feature of the limbus is:
	d -- stem cells The corneal epithelium is highly differentiated and renews rapidly.  For renewal, the corneal epithelium depends on stem cells, thought to be located in the limbal palisades of Vogt. The limbus is a barrier to separate the cornea and the conjunctiva. If limbal stem cells are injured, there is difficulty healing the corneal epithelium, and the conjunctival epithelium with goblet cells invades the cornea.
3.	The green stained layer contains:
	d -- (a), (b), and (c) The green stained layer contains lipid, aqueous, and mucin. The exact structure is controversial. The traditional concept is tripartite structure, with a superficial lipid layer 0.1 micrometers thick, aqueous layer 7 micrometers thick, and mucin layer 20-50 nanometers thick. Recent evidence suggests that the tear film is a mucin gel up to 40 micrometers thick. There is more mucin basally, and there is no discrete separation of the aqueous and mucin layers.