Regions and Layers of the Iris

Question 1

How many mm in diameter is the iris

Answer 1

12mm

Question 2

The iris is located slightly

Answer 2

Inferior-nasal

Question 3

Iris root

Answer 3

Peripheral region of the iris that is continuous with the ciliary body.

Question 4

Pupillary margin is positioned more ___ compared to the iris root

Answer 4

Anteriorly

Question 5

The pupillary margin rests where

Answer 5

On the crystalline lens. Without the support from the lens, the iris can become tremulous.

Question 6

Iridodenesis

Answer 6

When the lens is dislocated and the iris not longer receives support from it.

Question 7

Collarette

Answer 7

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)

Question 8

Thickest region of the iris

Answer 8

Collarette

Question 9

Attachment site for the fetal pupillary membrane (blood vessels) during development

Answer 9

Collarette. Vessels fragment and disappear by 8 and 1/2 months of gestation

Question 10

Persistent pupillary membrane

Answer 10

When there are remnants of the fetal pupillary membrane (blood vessels) projecting into the pupil hole.

Question 11

The collarette divides the pupil into which 2 zones

Answer 11

Divides the pupil into the pupillary zone (inner) and ciliary zone (outer)
The two zones may differ in color

Question 12

2 layers of the iris anterior to posterior

Answer 12

Anterior- Stroma (loose connective tissue)
Middle- Lesser pigmented single layer of epithelium
Posterior- Heavily pigmented single layer of epithelium

Question 13

The stroma is composed of what

Answer 13

Composed of loose connective tissue, pigmented cells (melanocytes and clump), WBCs, the spinster muscle, and extensions of the dilator muscle.

Question 14

In the iris stroma, the __ form a meshwork over the collagen and ground substance.

Answer 14

Fibroblasts.

Question 15

What is the role of collagen fibrils in the iris?

Answer 15

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.

Question 16

What contracts and what constricts

Answer 16

Muscles contract and the iris constricts

Question 17

Two types of pigmented cells in the iris stroma

Answer 17

1. Melanocytes- concentrated under the meshwork of fibroblasts
2. Clump cells. Scavengers of free pigment within the iris. Role similar to macrophages. Concentrated just under the meshwork of fibroblasts.

Question 18

Role and location of clump cells

Answer 18

Scavengers of free pigment within the iris. Role similar to macrophages. Concentrated just under the meshwork of fibroblasts.

Question 19

The sphinchter muscle within the iris stroma is compared of ____

Answer 19

Circularly arranged smooth muscle fibrils in the pupillary zone.

Question 20

Contraction of the sphincter muscle causes what to occur

Answer 20

Causes miosis (pupillary constriction). This pulls the pupillary zone towards the pupillary margin.

Question 21

Depressions in the pupillary zone and the ciliary zone of the iris stroma are called what

Answer 21

Depressions in the pupillary zone- Fuch’s Crypts

Depressions in the ciliary zone- Peripheral crypts

Question 22

What is the significance of Fuch’s and peripheral crypts within the iris stroma?

Answer 22

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.

Question 23

Dilator muscle of the iris arises from the basal surface of which layer

Answer 23

Arises from the basal surface of the anterior pigmented epithelium (middle layer that is less pigmented)

Question 24

The dilator muscle of the anterior pigmented epithelium basal surface is composed of

Answer 24

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.

Question 25

Contractions of the dilator muscle of the iris causes

Answer 25

Pupillary dilation (mydriasis) Pulls the pupillary zone towards the iris root. Circular contraction folds are visible in the ciliary zone, called contraction furrows.

Question 26

Contraction furrows

Answer 26

Folds visible in the ciliary zone. Occurs when the pupil dilates and the pupillary zone is pulled towards the iris root.

Question 27

Type of cell junctions in the pigmented epithelium of the iris

Answer 27

Both individual rows are held together by tight junctions.

The two layers join apex to apex.

Question 28

The anterior pigmented epithelium
The posterior pigmented epithelium

These layers are continuous with which layers in the ciliary body?

Answer 28

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.

Question 29

Which surface of the posterior pigmented epithelial cells of the iris line the posterior chamber?

Answer 29

The basal surface. Since the apex is joined with the apex of the anterior pigmented epithelial cells of the iris.

Question 30

How does the epithelium of the iris contribute to the blood/aqueous barrier?

Answer 30

Tight junctions join the adjacent pigmented epithelial layers.

This regulates the passage of aqueous humor from the posterior chamber into the iris root.

Question 31

Pupillary ruff/pupillary frill

Answer 31

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.