Choroid

Question 1

Where does the choroid extend from?

Answer 1

It is the most posterior portion of the uvea.
Extends from the ciliary body anteriorly to the margins of the optic nerve posteriorly.
Located between the sclera and the retina.

Question 2

Is chorioid thicker or thinner in myopes

Answer 2

Thinner.

Side note- diseases can thin or thicken chorioid

Question 3

Where is the chorioid thickest?

Answer 3

The fovea

Question 4

Main function of the choroid

Answer 4

To provide nutrients to and remove waste from outer rental layers (retinal pigment epithelium and photoreceptors).

Also absorbed light due to its heavy pigmentation.

May have a thermoregulatory role through heat dissipation.

Question 5

Composed of 3 regions (outer to inner)

Answer 5

Suprachoroid
Stroma
Choriocapillaris

Question 6

Suprachoroid

Answer 6

Potential space between the choroid and sclera. Transversed by thin, pigmented bands of loose connective tissue.
Provides a pathway for vessels and nerves to travel though to the globe.
Continuous with the supraciliaris, which is a potential space between the ciliary body and sclera.

Question 7

Stroma is composed of what cells

Answer 7

Composed of loose connective tissue (collagen, fibroblasts, elastic fibers, ground substance) with melanocytes and WBC

Question 8

Stroma is composed of which arteries and vessels

Answer 8

Arteries- These travel radially through the stroma. 
Short posterior ciliary arteries
Long posterior ciliary arteries
Anterior ciliary arteries
Vortex veins. 

Vessels- 
Large vessels (arteries and veins) are in the outer layer of the stroma (Haller's)
Medium vessels (arterioles and venules) are in the inner layer of stroma (Sattlers)

Question 9

Haller’s layer

Answer 9

Outer layer of the choroid stroma composed of large vessels- arteries and veins

Question 10

Sattler’s layer

Answer 10

Inner layer of the choroid stroma (closer to retina) composed of medium vessels- arterioles and venules

Question 11

Choriocapillaries location

Answer 11

Innermost region of the choroid (right by retina) composed of capillaries.

Question 12

Short posterior ciliary arteries form the ____ choriocapillaris

Long posterior ciliary arteries from the ____ choriocapillaris

Answer 12

Short posterior form the posterior

Long posterior form the anterior choriocapillaris

Question 13

How are the choriocapilaris different from normal capillaries?

Answer 13

They form a single layer of anastomosing capillaries.

They have a wide lumen that allows for 2-3 red blood cells to pass through next to each other (its normally single file).

Endothelial cells that composed the capillary walls deep to the retina are highly fenestrated with a discontinuous basement membrane. This allows for nutrients and oxygen to easily leak out and go to the retina. (RPE and photoreceptors)

Question 14

Blood flow in the choriocapillaris is significatnly higher than blood flow to other tissues. Why?

Answer 14

Blood flow is higher than in other tissues to meet the oxygen demands of the photoreceptor cells. The photoreceptor cells require 3-4x more oxygen levels than other CNS neurons.

Question 15

Where does blood go in the eye (3 places, %)

Answer 15

80% choroid
15% iris/ciliary body
5% retina

Question 16

Pericytes

Answer 16

Surround capillary walls and contract and alter local blood flow. Occasionally found in the choriocapillaris.

Question 17

Arrangement of choriocapillaris

Answer 17

Arranged in a lobular pattern. Has a feeding arteriole in the center of each lobule and venules in the periphery. Densest in the fovea where it is the sole blood supply.

Question 18

The basement membrane of the endothelial cells of the choriocapillaris forms ____

Answer 18

Bruch’s membrane

Question 19

Bruch’s membrane consists of….. (inner to outer)

Answer 19

For reference- Vitreous humor

1. Basement membrane of the Retinal pigmented epithelium.
2. Inner Collagen
3. Elastin
4. Outer Collagen
5. Basmenet membrane of endothelial cells of the choriocapillaris

For reference- Sclera

Question 20

What does OCT stand for

Answer 20

Optical coherence tomography

Question 21

Sensory innervation by CN V is by which mechanism

Answer 21

Via the nasociliary nerve branch: long ciliary nerves

Proprioception- awareness of the position and movement of the body. Not very specific. No nociceptors.

Question 22

How does sympathetic and parasympathetic innervation alter the size of the blood vessels in the choroid

Answer 22

Sympathetic- constriction

Parasympathetic- Vasodilation

Question 23

What does the nasociliary nerve of the trigeminal nerve innervate with its branches?

Answer 23

Infratrochlear- upper and lower lid/palpebral and fornicil conj

Long ciliary nerve- supplies bulbar conj, cornea, anterior sclera and choroid

Sensory root of ciliary ganglion- has a branch called the short ciliary nerves in the posterior sclera

Question 24

What does the long ciliary nerve supply

Answer 24

Bulbar conj, cornea, anterior sclera and choroid