Regions and Layers of the Iris Flashcards
How many mm in diameter is the iris
12mm
The iris is located slightly
Inferior-nasal
Iris root
Peripheral region of the iris that is continuous with the ciliary body.
Pupillary margin is positioned more ___ compared to the iris root
Anteriorly
The pupillary margin rests where
On the crystalline lens. Without the support from the lens, the iris can become tremulous.
Iridodenesis
When the lens is dislocated and the iris not longer receives support from it.
Collarette
Circular, jagged ridge 1.5mm from the pupillary margin. Thickest region of the iris.
Attachment site for the fetal pupillary membrane (blood vessels) during development. Vessels fragment and disappear by 8 and 1/2 months of gestation. There may be remnants (persistent pupillary membrane)
Thickest region of the iris
Collarette
Attachment site for the fetal pupillary membrane (blood vessels) during development
Collarette. Vessels fragment and disappear by 8 and 1/2 months of gestation
Persistent pupillary membrane
When there are remnants of the fetal pupillary membrane (blood vessels) projecting into the pupil hole.
The collarette divides the pupil into which 2 zones
Divides the pupil into the pupillary zone (inner) and ciliary zone (outer)
The two zones may differ in color
2 layers of the iris anterior to posterior
Anterior- Stroma (loose connective tissue)
Middle- Lesser pigmented single layer of epithelium
Posterior- Heavily pigmented single layer of epithelium
The stroma is composed of what
Composed of loose connective tissue, pigmented cells (melanocytes and clump), WBCs, the spinster muscle, and extensions of the dilator muscle.
In the iris stroma, the __ form a meshwork over the collagen and ground substance.
Fibroblasts.
What is the role of collagen fibrils in the iris?
They are arranged in radial columns, not evident in light-colored irises (appear as white fibers).
They anchor blood vessels, that also are arranged radially, in place and prevent the arteries from kinking and compressing as the iris constricts.
What contracts and what constricts
Muscles contract and the iris constricts
Two types of pigmented cells in the iris stroma
- Melanocytes- concentrated under the meshwork of fibroblasts
- Clump cells. Scavengers of free pigment within the iris. Role similar to macrophages. Concentrated just under the meshwork of fibroblasts.
Role and location of clump cells
Scavengers of free pigment within the iris. Role similar to macrophages. Concentrated just under the meshwork of fibroblasts.
The sphinchter muscle within the iris stroma is compared of ____
Circularly arranged smooth muscle fibrils in the pupillary zone.
Contraction of the sphincter muscle causes what to occur
Causes miosis (pupillary constriction). This pulls the pupillary zone towards the pupillary margin.
Depressions in the pupillary zone and the ciliary zone of the iris stroma are called what
Depressions in the pupillary zone- Fuch’s Crypts
Depressions in the ciliary zone- Peripheral crypts
What is the significance of Fuch’s and peripheral crypts within the iris stroma?
Allow aqueous humor to flow through the iris stroma during iris movement. This doesn’t create turbulence/waves in the aqueous humor when it moves.
Dilator muscle of the iris arises from the basal surface of which layer
Arises from the basal surface of the anterior pigmented epithelium (middle layer that is less pigmented)
The dilator muscle of the anterior pigmented epithelium basal surface is composed of
Radially arranged smooth muscle fibrils in the iris root to a point just below the sphincter. Forms 3-5 layers that extend into the stroma.
Contractions of the dilator muscle of the iris causes
Pupillary dilation (mydriasis) Pulls the pupillary zone towards the iris root. Circular contraction folds are visible in the ciliary zone, called contraction furrows.
Contraction furrows
Folds visible in the ciliary zone. Occurs when the pupil dilates and the pupillary zone is pulled towards the iris root.
Type of cell junctions in the pigmented epithelium of the iris
Both individual rows are held together by tight junctions.
The two layers join apex to apex.
The anterior pigmented epithelium
The posterior pigmented epithelium
These layers are continuous with which layers in the ciliary body?
The anterior pigmented epithelium is continuous with the pigmented epithelium of the ciliary body.
The posterior pigmented epithelium loses its pigment near the iris root and becomes continuous with the non pigmented epithelium of the ciliary body.
Which surface of the posterior pigmented epithelial cells of the iris line the posterior chamber?
The basal surface. Since the apex is joined with the apex of the anterior pigmented epithelial cells of the iris.
How does the epithelium of the iris contribute to the blood/aqueous barrier?
Tight junctions join the adjacent pigmented epithelial layers.
This regulates the passage of aqueous humor from the posterior chamber into the iris root.
Pupillary ruff/pupillary frill
Formed by both layers of the pigmented epithelium of the eye. Seen at the pupillary margin, 2 layers of epithelial cells curl around from the posterior iris to the anterior surface.
