Eye - Raised Intracranial Pressure Flashcards
what may cause a raised intracranial pressure (ICP)?
head injury
space occupying lesion, tumour, abscess or haemorrhage
hydrocephalus
meningitis
what are the 3 layers of meninges around the brain from outside to inside?
dura mater
arachnoid mater
pia mater
clinical sign on hydrocephalus?
sunset sign
- whites of eyes showing above the iris
how does hydrocephalus appear on imaging?
increased fluid in ventricles with thin layer of brain around them
how is the dura mater organised?
divided into the parts
can sometimes separate and venous blood can accumulate
describe the arachnoid mater?
middle layer
spider thin
has pool of CSF in large or small areas depending on folding
what is the thinnest layer of the meninge?
pia mater
only 1 cell thick
surrounds the brain, covering gyri and sulci
invisible to the naked eye
what are dural venous sinuses?
areas between layers of dura which hold venous blood
act the same as veins but not called veins as they don’t have a wall, instead they are between 2 layers of dura mater
how does the CSF drain into the venous blood?
goes through the arachnoid villi which penetrate into the dural venous sinuses
where will a double layer of dura mater be found?
where the dura mater moves away from the skull and envaginates into the longitudinal fissure
= falx cerebri
fold of dura mater separating the cerebrum from the cerebellum
tentorial cerebelli
what is the tentorial notch?
gap in dura mater surrounding the brain where the brainstem passes through
increased ICP can push the brain through the tentorial notch squishing important parts of the brain (eg can cause visual problems)
what does CSF do?
acts as a shock absorber for the brain
- brain floats in CSF which protects brain from trauma from hitting the skull
what are ventricles?
empty spaces within the brain
usually filled with fluid (CSF) during life
what are the 4 ventricles?
lateral ventricles (X2)
third ventricle
fourth ventricle
describe the 3rd ventricle?
between thalami
has a hole in the middle
drains via cerebral aqueduct
describe the 4th ventricle
between the pons and the medulla
what are the steps in CSF circulation?
choroid plexus > two lateral ventricles > intraventricular foramen > 3rd ventricle > cerebral aqueduct > 4th ventricle > median aperture/two lateral aperture/central canal of spinal cord
- median aperture > subarachnoid space > arachnoid villi > superior sagittal sinus
- two lateral apertures > subarachnoid space > arachnoid villi > superior sagittal sinus
what vessels are at risk from raised ICP?
veins which pass into the dural sinuses
what visual problems may occur in patients with raised ICP?
transient blurred vision double vision (diplopia) loss of vision papilloedema (swelling of optic disc due to increased ICP) pupillary changes
what supports the idea that the optic nerve is actually an extension of the brain?
covered by meninges
where does the subarachnoid space extend to?
the back of the eyeball
means raised ICP in the subarachnoid space can affect up until the eye
the subarachnoid space is between which 2 structures?
arachnoid and pia mater
what effects can raised ICP have on the eye?
can compress optic nerve
can compress central artery and vein of retina
can lead to bulging or swollen optic disc (papilloedema)
what visual symptoms may occur with raised ICP?
transient visual obscurations (greying out of vision) transient flickering bluring of vision contriction of the visual field decreased colour perception
how does CN III differ to CN IV and VI?
CN III has a parasympathetic component
which cranial nerves have a parasympathetic component?
III, VII, IX and X
what does CN III supply?
extrinsic muscles of the eye (most of them)
parasympathetic motor supply to the pupil (constrictor/sphincter pupillae muscle)
sympathetic supply to dilator pupillae muscles
motor supply to levator palpebrae superioris
damage to CN III may have what symptoms?
no/slow pupillary light reflex dilated pupil ptosis position of eye = looking down and out - parasympathetic function usually affected first as fibres are on the outside of the eye
what does the trochlear nerve supply?
superior oblique (superior oblique hooks round trochlear)
damage to the trochlear nerve (CN IV) can have what symptoms?
inferior oblique is unopposed = eye cannot move inferiomedially
diplopia when looking down
what does the abducent nerve supply?
lateral rectus (abducts the eye)
signs of CN VI damage?
eye cannot move laterally (abduct) in horizontal plane
medial deviation of the eye
what may cause a fixed dilated pupil?
damage to CN III parasympathetic fibres causing unopposed action of dilator pupillae which is supplied by the sympathetic fibres of CN III
