Blood Supply/Drainage of the Retina

Question 1

The outer 1/3 of the retina is supplied with blood by the

Answer 1

Choroid. The outer 1/3 is avascular.

The short posterior ciliary arteries form the posterior choroid.

The long posterior ciliary arteries and the anterior ciliary arteries from the anterior choroid.

Question 2

The inner 2/3 of the retina is supplied by

Answer 2

The central retinal artery.

15-20% of the population also have a cilioretinal artery to supply the inner 2/3 of the retina. Arises from the short posterior ciliary arteries.

Question 3

15-20% of the population also have a ______ to supply the inner 2/3 of the retina. Arises from the ______

Answer 3

Cilioretinal artery

Short posterior ciliary arteries.

Question 4

Which areas of the retina are only supplied by the choroid?

Answer 4

The extreme retinal periphery and the foveal avascular zone. Thin enough to be supplied by diffusion fro the choroidal circulation.

Question 5

Where is the middle limiting membrane located and what is it?

Answer 5

It is located in the outer plexiform layer. This layer is thought to perceive blood from both the choroid and central retinal artery.

Question 6

Choroidal vessels start ___ and project __

Central vessels start ___ and project ___

Answer 6

Outward and project inward

Inward and project outward

Question 7

Outer 1/3 of the retina is drained by which veins?

Answer 7

Choroidal veins that drain into Vortex veins. Choriocapillaris–> venules (Satler’s) –> Veins (Haller’s). Veins gather in 4-7 quadrants and exit the eye. Travel through the suprachoroidal space and pierce the sclera to drain into superior and inferior ophthalmic veins.

Question 8

Inner 2/3 of the retina is drained by which vein?

Answer 8

The central retinal vein. Deep capillary network –> venules —> 4 major beaches of veins within the GCL or NFL, which are ST, IT, SN, IN. The four branches join at the optic disc and travel with the ON Fibers and then leave the eye as a single vein (The central retinal vein). Drains into the superior ophthalmic vein or directly into the cavernous sinus.

Question 9

Course of the central retinal vein

Answer 9

Branches from the ophthalmic artery after it enters the orbit. Courses anteriorly a short distance before entering the meningeal sheath of the ON.

Continues anteriorly within the nasal portion of the ON to enter the globe.

Divides into 4 main branches- ST, SN, IT, IN

Question 10

After entering the globe, the central retinal artery travels where within the retinal layers?

Answer 10

3 capillary bed layers supply the outer retina.

1. The Superficial (inner) capillary bed located at the nerve fiber layer and ganglion cell layer.
2. The intermediate capillary bed located at the border of the inner plexiform and inner nuclear layers.
3. The Deep (outer) capillary bed located at the border of the inner nuclear and outer plexiform layers.

The Radial peripapillary bed supplies the optic nerve head.

Question 11

Around the fovea, the superficial and deep capillary networks of the central retinal artery form what

Answer 11

They anastomose to form a single layer that leaves the central 0.5 mm of fovea without vessels (FAZ)

Question 12

The superficial capillary bed of the central retinal artery is located where

Answer 12

At the nerve fiber layer and ganglion cell layer

Question 13

The intermediate capillary bed of the central retinal artery is located where

Answer 13

At the border of the inner plexiform and inner nuclear layers

Question 14

The deep capillary bed of the central retinal artery is located where

Answer 14

At the border of the inner nuclear layer and outer plexiform layer.

Question 15

The radial peripapillary capillary bed of the central retinal artery is located where and how does it project

Answer 15

Located at the optic nerve head and projects radially out from the ON

Question 16

Venous blood flow from the outer 1/3 retina

Answer 16

Outer 1/3
Choroidal veins
Vortex veins

Path 1:

1. Superior ophthalmic veins or inferior ophthalmic veins
2. Cavernous sinus
3. Petrosal sinuses
4. Right internal jugular vein
5. Right brachiocephalic
6. Superior vena cava.

Path 2:

1. Inferior ophthalmic veins
2. Pterygoid plexus
3. Maxillary vein
4. Retromandibular (to right internal jugular vein or external jugular)

Question 17

Venous blood flow from the inner 2/3 retina

Answer 17

Central retinal vein feeds into the superior ophthalmic vein- cavernous sinus- petrosal sinus- right internal jugular vein- right branchiocephalic- vena cava

OR the central retinal vein could feed directly into the cavernous sinus.

Question 18

The retromandibular vein can drain where?

Answer 18

Path 1:

1. External jugular vein
2. Right subclavian vein
3. Right brachiocephalic
4. Superior vena cava

Path 2:

1. Right internal jugular vein
2. Right brachiocephalic
3. Superior vena cava

Question 19

How to differentiate veins from arteries in the eye?

Answer 19

Veins are larger (more lumen) and darker (deoxygenated blood is darker red).

Question 20

Characteristics of veins in the eye

Answer 20

Very thin wall (which is atypical)
Appear darker and wider than arteries
Have a low hydrostatic pressure, which makes veins susceptible to occlusion if pressure is elevated.
No overlap in drainage. Nowhere for blood to go if occluded.

Question 21

AV crossing

Answer 21

If arteries cross over veins, they can press on the veins and cause occlusion. Especially if the artery is hardened due to cholesterol.

Question 22

3 contributions to the BRB

Answer 22

1. Tight junctions joining RPE cells. RPE cells controls what enters and exits the retina.
2. Capillary endothelial cells of the central retinal artery are joined by tight junctions.
3. Capillary endothelial cells of the central retinal artery are not fenestrated.

Question 23

Difference between central retinal artery and choriocapillaris

Answer 23

Choriocapillaris has fenestrations and no tight junctions.

Central retinal artery has no fenestrations and has tight junctions.

Question 24

The primary source of energy for the retina is provided by ___

Answer 24

Glucose metabolism. Glucose moves out of the capillaries and into retinal tissue via facilitated diffusion using a transporter protein.

Question 25

Which cells in the retina store glycogen

Answer 25

Muller cells. They provide a ready source of glucose to the retinal cells when they need it.

Question 26

Oxygen utilization by photoreceptors is ___ higher than other CNS neurons, therefore, most aerobic glucose metabolism occurs in photoreceptors.

Answer 26

3-4x. Allows more oxygen to diffuse out of the capillaries, across the RPE and into the mitochondria of the photoreceptor cells.

Question 27

To meet oxygen demands of the photoreceptors, what increases?

Answer 27

Blood flow to the choriocapillaris increases. Blood flow her is significantly higher than other tissues. (2000 ml/min vs 60 ml/min)

Question 28

Where do retinal cells get NADPH and what is it needed for?

Answer 28

Highly active pentose phosphate pathway generates NADPH through the oxidative phase. Needed for visual pigment regeneration.