Eye - Raised Intracranial Pressure

Question 1

what may cause a raised intracranial pressure (ICP)?

Answer 1

head injury
space occupying lesion, tumour, abscess or haemorrhage
hydrocephalus
meningitis

Question 2

what are the 3 layers of meninges around the brain from outside to inside?

Answer 2

dura mater
arachnoid mater
pia mater

Question 3

clinical sign on hydrocephalus?

Answer 3

sunset sign

- whites of eyes showing above the iris

Question 4

how does hydrocephalus appear on imaging?

Answer 4

increased fluid in ventricles with thin layer of brain around them

Question 5

how is the dura mater organised?

Answer 5

divided into the parts

can sometimes separate and venous blood can accumulate

Question 6

describe the arachnoid mater?

Answer 6

middle layer
spider thin
has pool of CSF in large or small areas depending on folding

Question 7

what is the thinnest layer of the meninge?

Answer 7

pia mater
only 1 cell thick
surrounds the brain, covering gyri and sulci
invisible to the naked eye

Question 8

what are dural venous sinuses?

Answer 8

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

Question 9

how does the CSF drain into the venous blood?

Answer 9

goes through the arachnoid villi which penetrate into the dural venous sinuses

Question 10

where will a double layer of dura mater be found?

Answer 10

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

Question 11

what is the tentorial notch?

Answer 11

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)

Question 12

what does CSF do?

Answer 12

acts as a shock absorber for the brain

- brain floats in CSF which protects brain from trauma from hitting the skull

Question 13

what are ventricles?

Answer 13

empty spaces within the brain

usually filled with fluid (CSF) during life

Question 14

what are the 4 ventricles?

Answer 14

lateral ventricles (X2)
third ventricle
fourth ventricle

Question 15

describe the 3rd ventricle?

Answer 15

between thalami
has a hole in the middle
drains via cerebral aqueduct

Question 16

describe the 4th ventricle

Answer 16

between the pons and the medulla

Question 17

what are the steps in CSF circulation?

Answer 17

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

Question 18

what vessels are at risk from raised ICP?

Answer 18

veins which pass into the dural sinuses

Question 19

what visual problems may occur in patients with raised ICP?

Answer 19

transient blurred vision
double vision (diplopia)
loss of vision
papilloedema (swelling of optic disc due to increased ICP)
pupillary changes

Question 20

what supports the idea that the optic nerve is actually an extension of the brain?

Answer 20

covered by meninges

Question 21

where does the subarachnoid space extend to?

Answer 21

the back of the eyeball

means raised ICP in the subarachnoid space can affect up until the eye

Question 22

the subarachnoid space is between which 2 structures?

Answer 22

arachnoid and pia mater

Question 23

what effects can raised ICP have on the eye?

Answer 23

can compress optic nerve
can compress central artery and vein of retina
can lead to bulging or swollen optic disc (papilloedema)

Question 24

what visual symptoms may occur with raised ICP?

Answer 24

transient visual obscurations (greying out of vision)
transient flickering
bluring of vision
contriction of the visual field
decreased colour perception

Question 25

how does CN III differ to CN IV and VI?

Answer 25

CN III has a parasympathetic component

Question 26

which cranial nerves have a parasympathetic component?

Answer 26

III, VII, IX and X

Question 27

what does CN III supply?

Answer 27

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

Question 28

damage to CN III may have what symptoms?

Answer 28

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

Question 29

what does the trochlear nerve supply?

Answer 29

superior oblique (superior oblique hooks round trochlear)

Question 30

damage to the trochlear nerve (CN IV) can have what symptoms?

Answer 30

inferior oblique is unopposed = eye cannot move inferiomedially
diplopia when looking down

Question 31

what does the abducent nerve supply?

Answer 31

lateral rectus (abducts the eye)

Question 32

signs of CN VI damage?

Answer 32

eye cannot move laterally (abduct) in horizontal plane

medial deviation of the eye

Question 33

what may cause a fixed dilated pupil?

Answer 33

damage to CN III parasympathetic fibres causing unopposed action of dilator pupillae which is supplied by the sympathetic fibres of CN III