Lecture 4 - The eye as a window to the CN Flashcards

1
Q

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

A

Neuronal – both have highly metabolically active tissues Vasculature – Blood neural barriers (BBB in brain and Blood Retinal Barrier in eye)

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2
Q

What advantages does eye assessment have over brain assessment?

A

-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.)

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3
Q

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

A
  • 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
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4
Q

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

A

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

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5
Q

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

A

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

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6
Q

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

A

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

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7
Q

What is fluorescein angiography?

A

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

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8
Q

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

A

Similar regulatory processes: autoregulation (constant blood flow)

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9
Q

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

A

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

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