NFL Flashcards
what is nerve fibre layer ?
- made of the axons of the ganglion cells as they run parallel to the retinal surface towards optic disc
why are ganglion cell axons un myelinated?
- ganglion cell axons of retina are not myelinated
- if they were myelinated , that would interfere with the process of light going through the retina
- axons in retina are un myelinated
what happens to axons in retina as they get to the optic nerve head?
- as soon as the axons in the retina get to the optic nerve head they become myelinated because ganglion cell axons have to go all the way to the brain and there you need myelination to speed up the process
- axons within optic nerve head are myelinated
what does the myelination of the optic nerve head result in ?
- in some people the myelination of the optic nerve intrudes into the retina at the optic disc resulting in a feathered edge to the optic nerve head
- not pathological condition
what is the size of axons that make up the nerve fibre layer ?
axons that make up the nerve fibre layer are half micron to 2/3 of micron in diameter depending on type of ganglion cells they came from
how does the thickness of the NFL change ?
- in the peripheral retina the NFL is thin
- near the optic nerve head NFL becomes very thick
why does the NFL become thick near the optic nerve head?
- the reason for the increased thickness of the NFL near the ONH is that the axons of peripheral ganglion cells are converging towards it
- in the periphery there are less axons but once you get closer to the optic nerve head all the axons run together making the nerve fibre layer thicker near the optic nerve fibre layer
what is the path taken by axons of retinal ganglion cells as they converge on the optic disc?
- in nasal retina the ganglion cell axons run directly towards the optic disc
- temporal fibres arc above and below fovea as they must avoid fovea
- axons from the foveola go
to optic disc in a straight line as the papillomacular bundle
what is the papillomacular bundle ?
- what attaches the fovea to the optic disc
what happens when you get a focal lesion in the retina ?
- focal lesion in the retina will disrupt all the axons running through that point, causing an area of blindness ( scotoma) over a wide area of the retina as peripheral areas will also be affected
what happens when you have a lesion of the nasal retina?
- will cause a wedge shaped scotoma
- even though a small part of the retina was destroyed many parts of the retina will be affected
- you will also go blind in area whose axons go through the focal lesion
what happens when you have a lesion of the temproal retina ?
- you will go blind in the temporal area and also go blind in area whose axons go through the focal lesion
- may cause an arcuate scotoma- as axons are arching above the fovea
what happens when you have lesions of the papillomacular bundle ?
- lesions of the papillomacular bundle are particularly severe, as they affect foveolar vision
explain the visual pathway ?
- 2 optic nerves coming out the eyes, behind the eye they come together at the optic chiasm
- they separate again and synapse in area known as lateral geniculate nucleus and then send fibres up to the primary visual cortex at the back of the head
what happens to the fibres nasal to the imaginary line that goes through the fovea?
those fibres nasal to an imaginary vertical line through the centre of the macular region cross over at the chiasm
