Function, Innervation, and Blood Supply of the Iris

Question 1

What occurs if bright light is shinned in the eye

Answer 1

Sphincter muscle contracts, dilator relaxes, and pupil constricts. This is under parasympathetic control.

Question 2

What occurs if you are in a room with dim light

Answer 2

Dilator muscle contracts, sphincter muscle relaxes, and pupil dilates. This is under sympathetic control.

Question 3

Pupil diameter varies from __ to __ mm

Answer 3

1-9mm

Question 4

What innervation plays a role in melanin production?

Answer 4

Melanocytes produce melanin when there is UV radiation. Sympathetic NS controls this.

Question 5

What color are babies eyes when they are born?

Answer 5

They are usually blue- blue/grey. During the first 6 months, melanocytes produce more melanin and the iris can darken.

Question 6

Heterochromia

Answer 6

2 different colored eyes.

Question 7

How could congenital horner’s syndrome affect eye color

Answer 7

Horner’s syndrome is the denervation/damage to sympathetic NS. Sympathetic NS regulates melanin production by melanocytes. If sympathetic cannot stimulate production, eyes will remain a light color. Other eye could darken.

Question 8

How is the iris innervated?

Answer 8

By CN 5. Opthalmic– nasocillary– long ciliary nerve and the short ciliary nerves

The short ciliary nerves are branches from the ciliary ganglion.

Question 9

What structures in the eye do the short ciliary nerves from the nasocilliary from the ophthalmic from CN 5 innervate

Answer 9

The short ciliary nerves innervates the posterior sclera and the iris.

Question 10

The long ciliary nerves from the nasocilliary branch off the ophthalmic off CN 5 innervates which structures in the eye

Answer 10

1. Cornea
2. Bulbar conj
3. Anterior sclera
4. Iris
5. Ciliary body
6. Choroid

Question 11

Blood supply to the iris

Answer 11

Highly vascularized.

Major arterial circle of the Iris (MACI) and the minor arterial circle of the iris supply the iris

Question 12

Are capillaries in the iris fennestrated or non fennestrated? How are they joined?

Answer 12

They are non fennestrated. They are joined by tight junctions

Question 13

How is blood drained from the iris?

Answer 13

Iris– Ciliary body veins— Choroidal veins– vortex veins –superior and inferior ophthalmic veins

Question 14

what artery forms the MACI

Answer 14

Long posterior ciliary arteries. Direct branches off the ophthalmic.
Supplies the ciliary body and the iris.

Question 15

Which 4 things contribute to the blood-aqueous barrier (prevents blood and cells from leaking into the anterior chamber)

Answer 15

1. Capillaries in the iris are non-fenestrated
2. Capillaries endothelial cells in the iris are connected by tight junctions
3. Tight junctions in the epithelial layers of the iris
4. Tight junctions in the non-pigmented epithelium of the ciliary body

Question 16

Minor arterial circle of the iris are formed by

Answer 16

They are formed from branches of the MACI (branch off muscular) that travel radially in towards the iris. The Minor arterial circle of the iris forms around the collarette.