CHOROID

Question 1

The choroid is thickest at which of the following locations?

Answer 1

Fovea

Question 2

Which of the following choroidal layers is directly internal to the sclera?

Answer 2

Suprachoroid

Question 3

Which of the following layers is continuous with the basement membrane of the RPE?

Answer 3

Basement membrane of the pigmented epithelium of the ciliary body

Question 4

If blood accumulates in the space between Bruch’s membrane and the RPE cells where might the blood have come from?

Answer 4

Choriocapillaris

Question 5

A sub-RPE hemorrhage is a term for the collection of blood between which 2 of the following layers?

Answer 5

Bruch’s membrane, Retinal pigmented epithelium

Question 6

What does the choroid help supply?

Answer 6

Outer layers of the retina, including the fovea

Question 7

What is the anterior-posterior extend of the choroid?

Answer 7

Extends from the optic nerve posteriorly to pars plana of the ciliary body anteriorly

Question 8

Where is the choroid the thinnest? Thickest?

Answer 8

Thicker posteriorly (thickest over fovea) and thinnest at ora serrata

Question 9

What lies in the suprachoroidal space?

Answer 9

The suprachoroid space is the outermost layer of the choroid. It is thin, with a delicate mesh of collagen fibers and melanocytes (no particular functional role)!

It is a space through which long & short posterior ciliary arteries and nerves (LPCA, SPCA, LPCN, SPCN) pass to reach the tissues they will innervate and supply with blood
– Running across the suprachoroidal space are thin sheets of pigmented connective tissue, called the lamina fusca (lamina suprachoroidea), which is one of the layers of the choroid.

Question 10

What are the 4 layers of the choroid?

Answer 10

1. Suprachoroid (also called: lamina fusca or lamina suprachoroidea)
2. Choroidal Stroma (Vessel Layer) = layer of large- & medium-sized blood vessels
   • Haller’s layer (arteries & veins)
   • Sattler’s layer (arterioles & venules)
3. Choriocapillaris (layer of capillaries)
4. Bruch’s membrane

Question 11

The blood vessels in the Haller’s layer are direct branches of these arteries:

a. anterior to the equator
b. at and posterior to the equator

Answer 11

a. Recurrent branches of both the LPCA & anterior ciliary arteries (supplying the choroid anterior to equator)

b. SPCA (supplying the posterior
portion of the choroid from the optic nerve to the equator of the eyeball)

The terminal branches of both the arteries in Haller’s layer & the arterioles in Sattler’s layer are “end- arteries” that only supply segments of the choroid. There are no anastomoses between segments at the arteriole level.

Question 12

The choriocapillaris receives blood directly from these blood vessels:
_____________ which are ________ (arteries? arterioles? capillaries?)

Answer 12

The choriocapillaris is the capillary bed of the choroid. It receives blood directly from arterioles in Sattler’s layer.

Question 13

How are choriocapillaris capillaries different from normal capillaries?

Answer 13

The capillaries of the choroid are amongst the largest in the body, measuring 20-50 μm in diameter so that several RBCs can pass through the lumen abreast, compared to ordinary capillaries through which they pass single file. They are also longer than normal capillaries.

Question 14

Describe the flow of blood from the choriocapillaris to the superior ophthalmic vein

Answer 14

VENOUS DRAINAGE
blood in the choriocapillaris → venules (in the Sattler’s layer) → choroidal veins in
Haller’s layer → vortex vein ampullae → vortex vein → superior or inferior ophthalmic veins

Question 15

What changes occur to Bruch’s membrane with increased age?

Answer 15

Everything that passes from the choroid to the retina and from the retina to choroid passes through Bruch’s membrane

Bruch’s membrane gradually thickens throughout life (i.e. as a person grows older) – The two collagenous layers become thicker
▪ The elastic layer may develop cracks & holes as a person gets older

Question 16

Name the 5 layers of Bruch’s membrane beginning nearest to the choriocapillaris

Answer 16

1. basement membrane of the endothelial cells of capillaries in choriocapillaris
2. outer collagen zone (for increased strength)
3. elastic zone (acts as shock absorber)
4. inner collagen zone (for increased strength)
5. basement membrane for the retinal pigmented epithelial cells (RPE)
   ▪ continuous with basement membrane of pigmented epithelium of ciliary body

Question 17

What is a serous RPE detachment and where is the serous fluid located?
Serous fluid lies between __________ & ________
Where did the fluid come from and how did it get to the location described above?

Answer 17

If breaks develop in Bruch’s membrane, fluid could leak from the choriocapillaris into the space between the RPE & Bruch’s membrane with resultant detachment of the RPE from Bruch’s membrane
– This is termed a serous “RPE detachment” wherein all 10 layers of the retina are pushed anteriorly towards the vitreous by the fluid

Serous fluid lies between Bruch’s membrane and RPE and might have come from the choriocapillaris through a break in Bruch’s membrane

Question 18

What is the anatomical reason why the RPE stays with Bruch’s membrane during a retinal detachment?

Answer 18

Fine filaments from the basement membrane of the RPE cells merge with collagen fibrils in the inner collagen zone, which helps maintain a strong adhesion between the RPE cells of the retina and Bruch’s membrane.

Question 19

Why does a sub-RPE hemorrhage appear gray-green in color? Where is the blood located? Be specific.

Answer 19

Because RPE cells are pigmented so we are looking at the blood through a pigmented layer

Question 20

The blood vessels in Sattler’s layer are direct branches of these arteries:

• anterior to the equator
• at and posterior to the equator

Answer 20

The choroidal stroma consists of loose connective tissue containing melanocytes & two layers of blood vessels:
– Haller’s layer - outer layer of large-sized blood vessels = arteries & veins
– Sattler’s layer - inner layer of medium-sized blood vessels = arterioles & venules

anterior to the equator: Recurrent branches of both the LPCA & anterior ciliary arteries
posterior to the equator: SPCA

Question 21

(CO) 1. Describe/discuss the choroid. Be sure to include:

• its 4 layers and their contents
• what blood vessels supply the choroid including (posterior part of the choroid, at and behind the equator and choroid anterior to the equator)
• venous drainage of the choroid as described on page 407 of the lecture notes
• its position in the eye and anatomical relationships to other parts of the eye
• areas where thickest and thinnest
• areas of eye that it helps to supply
• its functions

Answer 21

4 LAYERS
SUPRACHOROID

CHOROIDAL STROMA- loose CT + melanocytes and 2 layers of blood vessels: Haller’s (outer layer of large-sized blood vessels) and Sattler’s inner layer of medium arterioles/venules
-arteries in Haller’s give rise to arterioles in Sattler’s and similarly for veins; Sattler’s-> capillaries in choriocapillaris

CHORIOCAPILLARIS
largest capillaries in the body; with fenestrations (retinal saide) covered by diaphragm + complete basement membrane
-specialized to facilitate the rapid diffusion of fluids, oxygen, glucose, and macromolecules across the capillary endothelial cell membrane into the choroidal stroma and Bruch’s membrane.
-supplies the outer layers of the retina via diffusion of nutrients
-Selectivity due to zonula occludens junctions at the apical lateral borders of the RPE cells

BRUCH’S MEMBRANE
-metabolites from the choriocapillaris pass through Bruch’s membrane & then through the RPE cells of the retina; Waste products from the retina pass through the RPE cells & Bruch’s membrane tot he choriocapillaris where it is cleared to the venous circulation.
——————————————————————————-
FUNCTIONS
providing nourishment to the outer layers of the retina, including the fovea
– melanin in choroid absorbs any light that passes through the retina & is not absorbed by the photoreceptors & RPE cells
▪ reduces reflection of light back into eye by the sclera which would cause glare,
reduce contrast and reduce VA
– increased blood flow through the choroid helps protect the retina from thermal damage when light is focused on the retina or fovea, even under extreme conditions like arctic snow storms or looking at bright lights (like on a BIO)

Question 22

(CO) 2. Describe the suprachoridal (perichoroidal) and supraciliary spaces. Include:

• the structures they lie between
• what structures pass through the spaces
• know the 2 spaces are continuous with each other

Answer 22

Suprachoroidal = between choroid and sclera
Supraciliary = between ciliary body and sclera

SUPRACHOROIDAL
It is a space through which long & short posterior ciliary arteries and nerves (LPCA, SPCA, LPCN, SPCN) pass to reach the tissues they will innervate and supply with blood
Running across the suprachoroidal space are thin sheets of pigmented connective tissue, called the lamina fusca

SUPRACILIARY
long & short posterior ciliary arteries and nerves (LPCA, SPCA, LPCN, SPCN) pass forward through it to reach their target structures.

Question 23

(CO) 3. Name & describe the blood vessels (arterial & venous) in the vessel layer. Be sure to include:

• what blood vessels they originate from
• what blood vessels they give rise to
• what blood vessels the venous structures drain directly to

Answer 23

The choroidal circulation for the posterior choroid (supplied by the posterior ciliary arteries) is described as “lobular”. This means that the capillary bed of the choriocapillaris is composed of small independent lobules.

A central feeder choroidal arteriole (CA) gives off several precapillary arterioles (PA) that each supply an individual lobule.

• The precapillary arterioles enter the lobule centrally, so each lobule fills from its center to its periphery.
• The precapillary arterioles are functionally end arterioles, meaning they only supply that given lobule and no others.

Venous blood from each lobule is collected at the periphery of adjacent lobules & drains rapidly through venules that anastomose to create larger venules in Sattler’s layer & then they drain into veins in Haller’s layer.
The choroidal veins (CV) thus formed ultimately converge on several vortex ampullae.

Question 24

(CO) 4. Describe the capillaries in the choriocapillaris. Include:

• what vessels they originate from and drain into
• how they differ from normal capillaries in the body
• there characteristics of these types of capillaries
• where else in the eye this same type of capillary is seen

Answer 24

Marginal capillaries have the same histologic structure as choriocapillaris. They are needed for aqueous production.

Question 25

(CO) 5. Discuss where in the eye the capillary density of the choroid is highest and lowest, and why.

Answer 25

Capillary density is greatest at the fovea, where photoreceptor density is highest
– Cones are tightly packed at the fovea
• Capillary density is lower at the equator
• Capillary density is lowest at the periphery of the retina (i.e. near the ora serrata) where the retina is thinnest.

Depending on how much energy/nutrients is needed based on how metabolically active each part is

Question 26

(CO) 6. Discuss Bruch’s membrane. Be sure to include:

• description of its 5 layers and their contents
• anatomical location and relationships to RPE and choroid including: what is the anatomical reason why the RPE stays with Bruch’s membrane during a retinal detachment?
• functions
• what types of changes it undergoes with increased age

Answer 26

see previous question

Question 27

(CO) 7. Clinical correlations
Discuss what can happen if there are breaks in Bruch’s membrane. Be sure to include: what substances might pass through the breaks, where they come from, where they would specifically accumulate. See page 411 of lecture notes.
-How does one get a serous RPE detachment? (i.e. what had to be damaged? where is the fluid located (between what layers?) and where does the fluid come from?)
-How does one get a sub-RPE hemorrhage? (i.e. what had to be damaged? where is the blood located? Where did the blood come from? color of the blood and why that color?)

Answer 27

BREAKS IN BRUCH’S MEMBRANE
If breaks develop in Bruch’s membrane…

Fluid could leak from the choriocapillaris into the space between the RPE & Bruch’s membrane with resultant detachment of the RPE from Bruch’s membrane
> Might lead to serous “RPE detachment”
-wherein ALL 10 layers of the retina are pushed anteriorly towards the vitreous by the fluid
> Caused by blood accummulating between Bruch’s and RPE from the choriocapillaris (sub-retinal hemorrhage)

see previous question