Chapters 7-9 Flashcards
(185 cards)
what % of fibres in the anterior visual pathway serve central vision
90%
what makes up the anterior visual pathway
optic nerve
chiasm
tracts
what is a finding in many diseases of the optic nerve and anterior pathway
will cause red hues to become desaturated
what is an acceptable difference in pupil size?
less than 1mm is normal variation in 20% of the population
what is anisocoria
a difference in pupil size
what does a difference in pupil size (anisocoria) in DIM light indicate?
dilation SNS dysfunction–> HORNERS
what does a difference in pupil size (anisocoria) in BRIGHT light indicate?
abnormal constriction, PNS dysfunction–> 3rd NERVE PALSY, ADIE TONIC PUPIL
what does an RAPD almost always indicate
a leson in the optic nerve on the affected side or widespread/central retinal disorder (subtle)
do cataracts/vitreous hemorrhage affect pupillary reaction
no
does RAPD ever cause anisocoria
no, never
can RAPD ever be bilateral
no
what causes an RAPD
one optic nerve is less sensitive to light than the other
thus, the brain thinks the light to the normal eye is brighter than the light to the affected eye
when light is switched from the normal eye to the affected eye, the brain senses relatively less light in the affected eye and the affected pupil will DILATE
what is a mydriatic pupil
dilated pupil
with does a mydriatic pupil indicate
LOSS of PNS input to the iris sphincter
what can cause loss of PNS input to the iris sphincter (and thus cause a mydriatic pupil)
- oculomotor nerve paresis –> check with MRI
- benign ciliary ganglionopathy (adie tonic pupil)
- trauma to the orbital parasympathetic system (traumatic mydriasis)–> check with CT
- dorsal midbrain syndrome–> MRI
- prior iris damage/surgery
- pharmacologic
what does CN III do
controls pupillary sphincter muscles and some of the muscles of ocular movements
what happens when CN III is compromised
third nerve palsy
causes eyelid proptosis, pupil dilated and poorly reactive, eye loses ability to elevate, depress or move nasally
eye is turned OUTWARD and SLIGHTLY DOWNWARD
what direction does the eye point in a third nerve palsy
outward and slightly downward
how should you manage a new onset third nerve palsy
must undergo immediate, urgent MRI, CV imaging to rule out neural compression
what is the most common cause of third nerve palsy
circle of willis aneurysm
what usually causes a dilated fixed pupil in an otherwise healthy individual with normal ocular motility
usually benign and may be due to migraine, adie tonic pupil, dilating agents or secondary to previous ocular trauma
what is perinaud syndrome
dorsal midbrain syndrome
damage/compression to the upper brainstem
what causes dorsal midbrain syndrome/perinaud syndrome
can be caused by:
hydrocephalus
compressive lesion of the midbrain
MS
stroke
midbrain hemorrhage
what are the symptoms of dorsal midbrain syndrome/perinaud syndrome
loss of UPGAZE
convergence-retraction nystagmus
light-near dissociation of the pupils
eyelid retraction (collier sign)