week 1 the eye and ICP

Question 1

what is raised Intracranial Pressure? what two types are there?

Answer 1

Increase in pressure within the cranial cavity

Chronic or acute

Question 2

causes of RICP

Answer 2

Caused by an increased pressure in fluid surrounding the brain or an increase in pressure within the brain itself:

Brain tumour
Head injury
Hydrocephalus (increased fluid around the brain)
Meningitis
Stroke

Question 3

what is the problem with RICP?

Answer 3

Serious medical problem

Can cause damage to the brain and the spinal cord

Question 4

what is the The Monro-Kellie hypothesis ?

Answer 4

The intracranial volume is constant.

Brain, blood, CSF and any additional components (haematoma, tumour etc)

The cranial cavity is an enclosed space

It is not flexible or elastic

The space can’t increase to cope with an increase in pressure

Causes damage to tissues, shifts in tissues, herniation and constriction of blood vessels

Question 5

what visual problems to patients with RICP report?

Answer 5

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

(65-75% patients, affect one or both eyes)

Question 6

what are the optic nerves actually?

Answer 6

CNS tracts

Covered by meninges, Dura, Arachnoid, Pia

Question 7

what is the Space between arachnoid and pia called? why is this relevant?

Answer 7

Sub-arachnoid space

Filled with Cerebrospinal Fluid (CSF)

Question 8

what is the meninges?

Answer 8

Protective coverings of brain and spinal cord

Question 9

what does the meninges consist of (superficial to deep)

Answer 9

dura mater, arachnoid mater, subarachnoid space, pia

Question 10

describe the dura mater

Answer 10

“Hard mother”
Tough
Sensory supply from CN V
- Encloses dural venous sinuses

Question 11

describe the arachnoid mater

Answer 11

“Spidery mother”

Arachnoid granulations

Question 12

describe the subarachnoid space

Answer 12

Circulating CSF and blood vessels

Question 13

describe the pia

Answer 13

“Faithful mother”

Adheres to brain (and vessels and nerves entering or leaving)

Question 14

what does the Subarachnoid Space surround? what is its function?

Answer 14

completely surrounds both brain & spinal cord -
continuous

cushions and protects

Question 15

Subarachnoid Space contains what?

Answer 15

Contains circulating cerebrospinal fluid (CSF)

Question 16

where is CSF produced?

Answer 16

choroid plexus of the ventricles

Question 17

where is CSF reabsorbed?

Answer 17

into the dural venous sinuses, via arachnoid granulations

Question 18

how can the subarachnoid Space (and therefore CSF) be accessed?

Answer 18

via lumbar puncture at L3/4 or L4/5 IV disc levels [note:spinal cord ends L2 but dura continues until S2]

Question 19

what are the ventricles of the brain? where are they?

Answer 19

2 lateral (within the left and right cerebral hemispheres),

3rd (in the midline within the diencephalon)

4th (between the cerebellum & pons)

Question 20

how does CSF get from 3rd to 4th ventricle?

Answer 20

the cerebral aqueduct

Question 21

describe the circulation of CSF

Answer 21

secreted by the choroid plexus (epithelium/modified pia located in the lateral & third ventricles)→ right & left lateral ventricles→ 3rd ventricle→into cerebral aqueduct →4th ventricle→mainly into subarachnoid space→some passes into central canal→reabsorbed from the subarachnoid space via the arachnoid granulations (absorptive “herniations” of arachnoid mater protruding into the dural venous sinuses)
→into dural venous sinuses.

Question 22

how is the optic nerve affected by RICP?

Answer 22

Raised ICP will be transmitted along the subarachnoid space in the optic nerve sheath → compress CN 2 + central retinal artery and vein

Question 23

how is the optic disc affected by RICP?

Answer 23

Can lead to bulging or swollen optic discs = Papilloedema

Question 24

what visual symptoms arise from RICP?

Answer 24

• transient visual obscurations (graying-out of vision),
• transient flickering
• blurring of vision
• constriction of the visual field
• decreased colour perception

Question 25

how is the oculomotor nerve susceptible to damage?

Answer 25

Compression

Tentorial herniation

Question 26

what occurs is CN3 is damaged?

Answer 26

Paralysis of somatic motor innervation - 4 extra-ocular muscles and eyelid

Paralysis of parasympathetic innervation sphincter of pupil

lose/slowness of pupillary light reflex, dilated pupil, ptosis, eye turned inferolaterally
‘Down and Out’

Question 27

what two CNs come off the midbrain?

Answer 27

CN3 and 4

Question 28

what is CN 4

Answer 28

trochlear nerve

Question 29

what is the course of CN 4? how is it susceptible to damage

Answer 29

Long intracranial course - comes off back of midbrain, swamps sides and comes forwards.

susepctible to damage by stretching or compression

Question 30

what is see if CN 4 pathology?

Answer 30

Paralysis of superior oblique muscle

Inferior oblique is unopposed
eye cannot move inferomedially

diplopia when looking down.

• when walking to fix diplopia may till head=subtle sign of neck pain (as unopposed IO causes extortion)
• when doing down stairs cannot look down so may say blurry/tripping a lot

Question 31

what is CN 6? where does it come off? how can RICP damage it?

Answer 31

Abducent Nerve

comes off at junction between the pons and the medulla.

damaged by stetting

Question 32

what is see if CN 6 pathology?

Answer 32

Paralysis of lateral rectus muscle

Eye cannot move laterally in horizontal plane: - Medial deviation of the eye