ANATOMY - Iris

Question 1

What is the root of the iris?

Answer 1

Insertion of the iris to the ciliary body and it is thinnest here.

Question 2

What is iridodialysis?

Answer 2

At the thinnest point, root of the iris becomes detached and causes a D shaped pupil

Question 3

What is the diameter of the iris?
What is the diameter of the pupil?

Answer 3

1. 12mm
2. 3-4mm

Question 4

What is the thickness of the iris?

Answer 4

0.5mm

Question 5

What is the collarette of the iris?

Answer 5

2mm from pupillary margin is a zig zag line which divides anterior iris into 2 zones (ciliary and pupillary zone) and represents attachment of pupillary membrane

Question 6

What are the important structures of the ciliary zone/outer zone of the iris (2)

Answer 6

Radial streaks correspond to radial streaks and become wavy when pupil is dilated
Contraction furrows are faint lines parallel to colarratte
Crypts : absent anterior layers

Question 7

What are the layers of the iris (4)

Answer 7

1. Anterior limiting membrane
2. Stroma
3. Anterior pigmented epithelium
4. Posterior pigmented epithelium

Question 8

What is contained in the anterior limiting layer?

What substance can penetrate through this?

Answer 8

Consists of melanocytes and fibroblasts - decides the colour of the iris.
—> thin/few melanocytes - blue iris
—-> thick/many melanocytes - brown/black iris

This layer is absent in crypts and thin in furrows

Aqueous can penetrate through this layer into the stroma as it is not a true epithelium

Question 9

What happens in iris heterochromia / Fuch’s uveitis? (2)

Answer 9

Progressive atrophy of the anterior layer and stroma of iris –> loss of iris colour

Transillumination defects
Blurring of iris crypts (darker individuals)

Question 10

What is contained within the iris stroma ? (6)

Answer 10

1 Network collagen
2. Ground substance
3. Sphincter Pupillae
4. Dilator Pupillae
5. Vessels and nerves
6. Pigment

Question 11

Where is sphincter pupillae derived from?
Where is dilator pupillae derived from?

Answer 11

Sphincter - ectoderm
Dilator - myoepithelium

Question 12

What is the nerve supply of the sphincter and dilator pupillae?

Answer 12

1. SPHINCTER - parasympathetic post-ganglionic fibres of third nerve via short ciliary nerve
2. DILATOR - sympathetic cervical chain via long ciliary nerve

Question 13

Where is the sphincter pupillae located?
Where is the dilator pupillae located?

Answer 13

Sphincter - pupillary zone (inner zone)
Dilator - Ciliary zone near iris root

Question 14

What are the main vessels of the iris?
What characteristics do they have? (2)

Answer 14

Radial branches of major arterial circle, responsible for formation of radial furrows

1) Lack internal elastic lamina
2) Have non fenestrated endothelium

Question 15

What is contained within the anterior epithelium of the iris?

Answer 15

Pigmented layer containing origin of dilator pupillae muscle

Question 16

What is contained within the posterior pigmented epithelium of the iris

Answer 16

At pupillary margin, forms the pupillary frill and meets anterior epithelium

Question 17

What is the difference between seclusio pupillae and occlusio pupillae?

Answer 17

Seclusio - 360 degrees synechiae
Occlusio - 360 degrees synechiae with lens not visible (fibrin formation)

Question 18

What is the function of the iris capillaries?

Answer 18

Form the major site of blood-aqueous barrier.

Question 19

What is the structure of iris capillaries (3)

Answer 19

1) Non-fenestrated
2) connected by tight junctions
3) have thickened basal lamina strengthened by perivascular collagenous hyalinised layers

Question 20

What’s the difference in epithelium of the iris and ciliary body?

Answer 20

1. Both bilayered. Only iris has both epithelia pigmented, ciliary body has outer layer pigmented,inner layer is not pigmented