L06 - The eye as a window to the CNS Flashcards Preview

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Flashcards in L06 - The eye as a window to the CNS Deck (9)
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1

How it the eye similar to the brain – neuronally and vascularly?

Neuronal – both have highly metabolically active tissues

Vasculature – Blood neural barriers (BBB in brain and Blood Retinal Barrier in eye)

2

What advantages does eye assessment have over brain assessment?

-Non-invasive
-Inexpensive relative to PET/MRI
-Simpler to analyse/interpret: relatively 2D instead of 3d
-Simple and rapid to conduct “photo” (in brain assessment, takes hours, can’t wear metal objects, no food etc.)

3

Besides the retina being part of the CNS (embryonically retinal extension of diencephalon), how are photoreceptors similar to CNS neurons?

- Both highly metabolically active tissue – photoreceptors most metabolically active tissue/weight
- Similar support cells = glia
- Similar NT: Glu, glycine, dopa, NMDA, GABA
- Similar age-related decline/neurodegeneration: Healthy aging, Alzheimer, Parkinsons

4

!Similarities between blood neural barriers between the eye and the brain? Mechanical barrier? Metabolic barrier

Both protect neurons, regulate substances from blood
Mechanical barrier: formed by tight junctions
1) Occludin
2) Claudins
3) Junctional adhesion molecules (JAM)
Metabolic barrier:
1) Glucose transport mechanisms: GLUT1 and 3
2) Specific a.acid protein transport systems

5

!The retina has an inner and outer blood supply and an inner and outer barrier - what are these 2 blood supplies and 2 barriers?

BLOOD SUPPLY
Inner (60-80%): central retinal artery/vein (thinner) - supplies GC & BC
Outer (20-30%): Choroid - supplies Photoreceptors
BARRIER
Inner: endothelial cell tight junctions in vasculature
Outer: RPE tight junctions that prevent blood from leaking into the neurons

6

Inner BS:
The tight junctions are located around the capillaries which are in between the endothelial cells of the capillaries

Outer BS:
Choriocapillaris have more gaps between the endothelial cells - more leaky

Inner BS:
The tight junctions are located in between the endothelial cells of the capillaries

Outer BS:
Choriocapillaris have more gaps between the endothelial cells - more leaky

7

What is fluorescein angiography?

Venous injection of fluorescent dye that highlights breakdown of blood retinal barrier
-> As the dye is a large molecule, it will stay within the retinal vasculature as it cannot penetrate through the retinal blood barrier

8

Similarities in vascular regulation (inner retinal circulation and cerebral circulation) between eye and brain

Similar regulatory processes: autoregulation (constant blood flow)

9

As the eye is the only place where microvascular system can be directly visualised, it is a marker for diseases such as?

Diabetes
-Loss of retinal pericytes (cells that are on the outside of the endothelial cells - this leads to leaking of blood retinal barrier)
-Basement membrane thickening
-Capillary microaneurysm (swelling) formation
-Increased vascular permeability such as exudation (fluid oozing) and tissue oedema
-Ischemia lead to retinal neovascularization (formation of new blood vessels - if they don’t have proper blood retinal barriers, they just leak and make things worse)

Hypertension
-generalized retinal arteriolar narrowing
-arteriovenous nicking (artery squashing overlapping vein due to increased BP) and arteriolar tortuosity (curly)
-blood retinal barrier breakdown (haemorrhages, exudates, nerve fibre ischemia - cotton wool spots)

Stroke
Predictor of stroke is quantitative by measuring vessel diameter

Multiple sclerosis: inflammatory demyelinating disease
-Retinal nerve fibre layer (where GC axons exit) thinning in MS patients
-Occurs with optic neuritis (also seen in MS patients that don’t have ocular disease)
-Can be assayed using optical coherence tomography (like US except shorter wavelengths - this means higher res using this technique)

Alzheimer’s - IN THE FUTURE
At the moment, current definitive diagnosis is post-mortem Alpha beta plaques or PET imaging
HOWEVER recently retinal Alpha Beta plaques are also seen in Alzheimer’s patients