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
in dark- pupil dilatation-which nerve is it mediated by and cause which muscle to contract
sympathetic nerve
contract radial muscle
explain the pupillary reflex steps
afferent-
1. pupil-specific ganglion cells exit optic tract (before LGN)
2. synapse at brainstem pretectal nucleus
3. synapse at Edinger-Westphal Nuclei on both sides in brainstem
efferent-
4. Edinger-Westphal nucleus–> oculomotor nerve efferent
5. synapse at ciliary ganglion
6. short posterior ciliary nerve –> pupillary sphincter
what is it called when pupil constrict from direct light stimulation vs constriction of pupil in the other eye
direct vs consensual pupillary reflex
what is the swinging torch test for (hint- damage to afferent pathway is usually incomplete/relative). How to do the test?
relative afferent pupillary defect
-alternating stimulation of right and left eye with light
results of swinging torch test if
left=undamaged
right=damaged (relative-afferent pathway)
-both pupils constrict when light swings to left undamaged side
-both pupils paradoxically dilate when light swings to right damaged side =positive sign
what nerve innervates lateral rectus and superior oblique
lateral rectus= CN 6- abducens
superior oblique= CN 4- trochlear
