POSTERIOR SEGMENT - Choroid

Question 1

What is the choroidal thickness posteriorly? What is the choroidal thickness anteriorly?

Answer 1

posterior - 0.2mm
anterior - 0.1mm

Question 2

What are the layers of the choroid from outside to inside? (4)

Answer 2

Suprachoroidal lamina (lamina fusca)
Choroidal stroma (Haller’s and Sattlers)
Choriocapillaries layer (Ruysch)
Bruch’s membrane –> RPE

Question 3

What is the lamina fusca? What is it connected to anteriorly? What space is in this layer? (3)

Answer 3

Thin condensed membrane of choroidal stroma

Continuous anteriorly with supraciliary lamina of the ciliary body

Space between here and sclera is the suprachoroidal space - useful for drug delivery

Question 4

What does the choroidal stroma consist of? (3)

Answer 4

1. Framework of collagen, elastin and reticular tissue with pigment cells and other cells
2. Outer Hallers layer - large diameter vessels
3. Inner Satler layer - intermediate size vessels

Question 5

What type of endothelium does the choriocapillaries have? What is it surrounded by?

Answer 5

1. Fenestrated endothelium
2. Basement membrane and pericytes

Question 6

Where is the highest density of the choriocapillaries?

Answer 6

Highest in the macular area - thickest here at 10um

Question 7

How much ocular blood flow does the choriocapillaries receive? How much oxygen extraction?

How much ocular blood flow does retina receive? How much oxygen extraction?

Answer 7

1. 65-70% of ocular bloodflow - 3% of oxgen
2. 5% of ocular blood flow - 38% of oxygen extraction

Question 8

What are the reasons of slower blood flow in the choriocapillaries (5 times slower)

Answer 8

Large lumina of the choriocapillaries
Large blood volume in choroid
Lobular configuation of the choriocapillaries

Question 9

What are the 5 layers of the Bruch’s membrane? Inner to outside

Answer 9

Basement membrane of RPE
Inner Collagenous layer
Elastic Layer - anti-angiogenic property
Outer collagenous layer
Basement membrane of choriocapillaries

Question 10

What are the structures involved in the outer blood retinal barrier?

Answer 10

Bruch’s membrane
Tight junctions of RPE

Prevent leakage of fluid from choroid into the retina

Question 11

What are the functions of the uvea? (6)

Answer 11

1. Source of blood flow to outer 4 layers of retina (outer plexiform layer, outer nuclear layer, IS/OS zone and RPE)
2. Source of aqueous humor production
3. Ciliary muscle helps as accomodation
4. Acts as thermal sink of the eye (choriocapillaris, sattler’s, hattlers)
5. Production of eicosanoids of eye

6.Anti-oxidant properties

Question 12

What is choroidal thickness? Thickest at ….

Answer 12

Choroidal thickness is 100-200um
Thickest at posterior pole