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What does the iris divide?
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The space between the cornea and the lens into the anterior and posterior chambers
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Pupil:
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Hole in the iris, located slightly nasal and inferior. Diameter can range from 1-8 mm
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Average width of the iris:
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12 mm: thickest in the collarette region, thinnest at the iris root.
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Iris Collarette
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Ridge approximately 1.5mm from the pupillary margin that serves as a site of attachment for fetal pupillary membrane during embryonic development. Divides the iris into pupillary and ciliary zones.
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What are the four cellular layers of the iris (front to back)
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1. Anterior border layer2. Iris stoma3. Anterior epithelium and dilator muscle4. Posterior pigmented epithelium.
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Anterior border layer of the iris: What does it provide?
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Provides definitive color to the iris. In the blue iris, the anterior border layer is thin with only a few pigment cells, in the brown iris it is thick and densely pigmented. Contains fibroblasts and melanocytes. This layer extends all the way down to the iris root.
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Where are iris crypts? what are they?
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They are in the anterior border layer. The are collagenous columns that serve as passageways for aqueous to ender the stroma. This gives the anterior iris surface a rough appearance. No tight junctions are located in this region.
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What is iris color dependent on?
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The amount of melanin within melanocytes in the anterior border layer and stroma (stroma is a minor contributer). Heterochromia denotes a difference in iris color between eyes. It can be congenital or due to other factors, such as topical prostaglandin use or chronic inflammation (i.e. uveitis)
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Iris stroma:
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Loose collagen network with fewer cells than the anterior border layer. Continuous with the stroma of the ciliary body. Contains 3 important elements
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What are the 3 important elements of the iris stroma?
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1. Nerves: CNIII (LPCN and SPCN)2. Blood vessels: iris capillaries are non-fenestrated (with zonulae occludens junctions) and form part of the blood-aqueous barrier. Major circle of the iris: located in the ciliary body close to the iris root: extends radially through the iris stroma up to the pupillary marginMinor circle of the iris: located in the iris stroma at the level of the collarette. 3. Spinctor muscle: Circular smooth muscle anchored firmly in the stroma. Innervated by SPCN's for parasympathetic control and pupillary constriction.
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Where is the major circle of the iris located?
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Located in the CB close to the iris root: it extends radilly through iris stroma up to the pupillary margin
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Where is the minor circle of the iris?
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Located in the iris stroma at the level of the collarette
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What innervates the sphinctor muscle of the iris?
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It is under parasympathetic control from the short posterior ciliary nerves.
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Anterior epithelium of the iris:
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Contains myoepithelial cells: This epithelium lies closest to the iris stroma. Extends posteriorly to become the pigmented epithelium of the ciliary body.
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Dilator muscle of the iris:
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Extends from the iris root into the pupillary zone and terminates at approximately the midpoint of the sphincter. Extends radially, so simpathetic innervation (dilation) pulls the pupillary portion toward its origin at the iris root.
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