Vision 2 Flashcards
What is the point at which central retinal artery and vein pierce the eyeball called?
Lamina cribrosa (sieve like thinned area)
What branch does the internal carotid artery give to the eye?
Ophthalmic artery - which then branches into central retinal artery
What part of the eye is supplied by the central retinal artery?
inner 2/3 retina
What structures pass through lamina cribrosa?
optic nerve
central retinal artery and vein
What is the most common cause of a blockage in the central retinal artery?
clot travelling from internal carotid
Are arteries or veins thinner in the eye?
arteries
What are the four divisions of the central retina artery when it enters the eye?
- superotemporal
- inferotemporal
- inferonasal
- superonasal
What blood vessels supply the rest of the retina (not supplied by central retinal artery)?
choroid
What can occur to the fovea in diabetes
foveal avascular zone increases as you get capillary dropout
How does raised ICP affect the eye?
pressure is transmitted along the subarachnoid space which is found around the optic nerve
resulting in compression of the central retinal vein causing papilloedema
What three things should be described when checking the optic disc?
Colour
Contour
Cupping
If the contour of the optic disc is indistinct what does this mean?
disc is swollen which often occurs in raised ICP
What colour should the optic disc rim be?
Orange, if there is a pathology will change to be pale
What are the branches of the ophthalmic artery?
Central retinal ciliary arteries - long posterior ciliary - short posterior ciliary - anterior ciliary
What does the ciliary arteries supply?
Uvea (choroid, ciliary body + iris)
At what point does the retina stop anteriorly?
Ora serrata
What is the name of the membrane found between the retina and choroid?
Bruck’s membrane (part of Retina) just outisde the RPE cells
How do the RPE cells connect to the photoreceptor cells?
Axons of the RPE
What two factors prevent opening of the space between photoreceptors and RPE cells (sub retinal space)
- pumping out of water by RPE cells creates negative pressure pulling them together
- glycosaminoglycans (act as glue)
What allows the RPE to create a blood brain barrier?
have tight junctions
What substances does the RPE cells take up from the general circulation?
- glucose
- retinal
- specialised phospholipids used in creation of photoreceptors
Why is RPE so oxidative?
RPE take up parts of old photoreceptors and breaks them down using lysosomes & in the process releasing free radicals
What is the function of the choroid outside of O2 and nutrient deliver?
- take heat away
- melanosomes (pigment granules) absorb light and heat up as result
Describe the initiation of the visual cycle in rods
- photon of light absorbed by 11-cis retinal (in photoreceptors)
- this causes change in conformation of 11-cis retinal (called bleaching)
- creates all-trans retinal & free opsin
- RPE (not photoreceptors) reform 11-cis retinal
How does creation of opsin result in visual signal being sent along visual pathway?
- opsin closes Na channels on outer segment of photoreceptors
- Na usually allowed to flow freely into photoreceptors
- blocked so Na in cells fall and transmembrane potential fall
- hyper-polarisation is transmitted along visual pathway
What is the function of RPE?
- absorb light
- phagocytose photoreceptor segments
- secretes VEGF (vascular endothelial growth factor)
What is the function of VEGF?
keep capillaries of choroid fenestrated (and leaky)
What cells must the AP pass through to get from photoreceptor to optic nerve?
photoreceptor (rod & cone) (horizontal cells) 1) bipolar cells 2) Amacrine cells 4) ganglion cells (axons of these stream toward optic nerve)
How should dark and light areas of an OCT be described?
Hypo-reflexive (dark)
Hyper-reflexive (light)
What is the pathway of the optic nerve from the eye to optic chiasm?
1) when first leaves eyeball orbital portion passes posteriorly through optic canal (hole in sphenoid bone)
2) Intracranial portion moves upward and backward toward floor of third ventricle
3) where meets the optic nerve of the opposite side at optic chiasm
What aspects of your vision would a pituitary tumour affect?
temporal vision in both eyes
What is the pathway of the optic nerve from the chiasm to primary visual cortex?
- travel posterolaterally
- fibres synapse at LGB (lateral geniculate body)
- optic radiation part of optic nerve passes from LGB to primary visual cortex
What would be the visual impairment if there was a lesion in the optic chiasm?
bitemporal hemianopia
lose peripheral vision in both eyes, still have central vision
What would be the visual impairment if there was a lesion in the right optic nerve?
total right eye visual loss
What would be the visual impairment if there was a lesion in the left optic nerve after chiasm?
right homonymous hemianopia
lose right side of vision in both eyes
What would be the visual impairment if there was a lesion in the right side optic radiation?
left homonymous hemianopia with macular sparing
lose vision in left side of both eyes
Where do optic nerve fibres first synapse?
90% synapse at LGB Lateral geniculate body
10% synapse at pretectal nucleus
Why do both pupils constrict in the pupillary light reflex?
after those 10% of fibres divert before the LGB to synapse at the pretectal nucleus they travel to Edinger Westphal nucleus (EWN) on both sides which then travels via CN3 to ciliary sphincter
