Neuro-visual System Flashcards
what is the limbus
border between cornea and sclera
what are the 3 layers of the eye and brief functions
sclera= hard and opaque
choroid= pigmented and vascular coat
retina= neurosensory tissue
what does the uvea contain and it’s function
vascular coat
iris, ciliary body and choroid
-one part affects the other (in disease)
retina function
captures light rays- light impulses sent to brain via optic nerve
macula
where is it to optic nerve?
function?
what is at the centre?
-temporal to optic nerve
-detailed central vision
-fovea- give detail ventral vision ie. reading
what is a blind spot
where optic nerve meets retina- no light sensitive cells.
optic nerve meeting retina- what is it called
optic disc
what does the central vision involve-
which photoreceptor dominates?
how to assess
what happens when foveal vision is lost
detail/colour vision
-cone receptor
-visual acuity assessment
foveal lost= poor visual acuity
what does the peripheral vision involve-
how to assess ?
what happens when visual field is lost?
movement and night vision
-visual field assessment
-unable to navigate- may need white stick even with perfect visual acuity
Retinal structure what is in the
outer layer
middle layer
inner layer
- and what each does
outer layer
- photoreceptors-1st order neuron
-detect light
middle layer
- bipolar cells (2nd ON)
-local signal processing
inner layer
-retinal ganglion cell (3rd ON)
-transmission of signal from eye to brain
photoreceptor- what is rods
-more sensitive to light
-slow response to light
-night vision
-most abundant
photoreceptor- what is cones
less sensitive to light but faster response
-day light fine (+colour) vision
what is emmetropia
adequate correlation between axial length and refractive power
-parallel light rays fall on retina
what is it called when there is a refractive error-
mismatch between axial length and refractive power- parallel light doesn’t fall on retina?- overall terminology
ametropia
what is myopia and causes
Parallel rays converge at focal point anterior to retina.
Causes
-excessive long globe (axial myopia)-common
-excessive refractive power (refractive myopia)
myopia symptoms
Blurred distance vision
Squinting
Headache
what is hyperopia and causes
Parallel rays converge at a focal point posterior to the retina
Causes
-excessive short globe (axial hyperopia) :common
-insufficient refractive power (refractive hyperopia)
hyperopia symptoms
blurring at close distance
eye pain/headache
what is the near response triad
-pupillary miosis- sphincter pupillae=increase field depth
-convergence -medial recti
-accommodation - circular ciliary muscle= increase lens refractive power
all contracts
presbyopia what is it? age of onset?
how is it corrected ?
-natural loss of accommodation.
-40y.o +
-corrected by reading glasses (convex)- increase refractive power.
Visual Pathway Anatomy
- eye
- optic nerve
- optic chiasm
- optic tract
- lateral geniculate nucleus (thalamus- synapse)
- optic radiation=4th order neuron
- primary visual cortex
common causes of homonymous hemianopia
stroke
why is there macular sparing in some homonymous hemianopia
damage to primary visual cortex
-ie stroke
-macula receives dual blood supply from posterior cerebral arteries from both sides
in light- pupil constrict-> which nerve is it mediated by and which muscle contract
parasympathetic nerve (CN III)
contract circular muscle
