1.9: The Eye and Raised ICP

Question 1

What is raised ICP? Types?

Answer 1

This is raised pressure in the cranial cavity Chronic or acute

Question 2

Causes of raised ICP?

Answer 2

Increased pressure in fluid around brain (CSF) or increased pressure within brain itself

• Brain Tumour
• Head injury
• Hydrocephalus
• Meningitis
• Stroke

Question 3

Is raised ICP a medical emergency? If yes, why?

Answer 3

Yes Because it can cause damage to the brain, spinal cord and the eyes

Question 4

Describe the components of ICP?

Answer 4

ICP is the sum of:

• Blood
• Brain
• CSF

Question 5

Describe how the ICP is kept constant?

Answer 5

If one component increases, the others decrease to compensate and keep the ICP constant (and vice versa)

Question 6

Describe the monro-kellie hypothesis?

Answer 6

If one component of ICP increases, the others decrease the compensate and keep the ICP constant (and vice versa)

Question 7

Describe the cranial cavity in regards to ICP?

Answer 7

The cranial cavity is an enclosed space and is unable to expand as the pressure increases

Question 8

Describe the relationship between ICP and volume?

Answer 8

As volume increases, compensatory mechanisms are able to prevent the pressure from rising After compensatory mechanism fail, a small change in volume will cause a large change in pressure (exponential)

Question 9

Increased pressure can lead to damage Give examples?

Answer 9

Damage to tissue

Shifts to tissue

Damage to brain, spinal cord and eye

Herniation

Constriction of blood vessels

Question 10

Describe a statistic that links raised ICP and visual symptoms?

Answer 10

65% of patients with ICP will complain of some visual symptoms

Question 11

Examples of visual symptoms caused by raised ICP?

Answer 11

Transient Blurred Vision Doubled Vision Loss of Vision Papilloedema (Swelling of optic discs due to raised ICP) Pupillary changes Can affect one eye or both

Question 12

Optic nerves are not actually nerves but they are…?

Answer 12

CNS Tracts

Question 13

What covers optic nerves?

Answer 13

3 Meninges: - Dura - Arachnoid - Pia

Question 14

What is the space between the Arachnoid and Pia called?

Answer 14

Sub-arachnoid space

Question 15

What are meninges?

Answer 15

These are the three membranes than envelope the brain and the spinal cord - they are the protective coverings

Question 16

Describe the Dura Mater? Sensory supply?

Answer 16

This is the tough, outer meningeal layer Sensory supply is CN V Encloses dural venous sinuses

Question 17

Describe the arachnoid mater?

Answer 17

This is the spidery mother Has lots of little projections called ‘arachnoid granulations’

Question 18

Describe the subarachnoid space?

Answer 18

This is space below the arachnoid mater There is circulating CSF and blood vessels

Question 19

Describe the pia?

Answer 19

This is the faithful mother Adheres to the brain Also adheres to vessels and nerves that are entering/leaving the brain

Question 20

Label this diagram?

Answer 20

A = Pia B = Arachnoid Layer C = Dura D = Dura

Question 21

How do you access the subarachnoid space?

Answer 21

Lumbar puncture between L3/L4 or L4/L5

Question 22

Where does the subarachnoid space end?

Answer 22

At the level of S2 (Part of the Sacrum)

Question 23

Label this diagram?

Answer 23

A = Subarachnoid Space B = Dura C = Arachnoid D = Pia

Question 24

The subarachnoid space communicates with another series of CSF filled spaces in the brain. What are these called?

Answer 24

The Ventricles

Question 25

Name the ventricles of the brain?

Answer 25

3rd 4th Left Lateral Right Lateral

Question 26

Label this diagram?

Answer 26

A = Third Ventricle B = Left Lateral Ventricle C = Right Lateral Ventricle D = Subarachnoid Space E = Central Canal of the Spinal Cord F = 4th Ventricle G = The Cerebral Aqueduct H = Pituitary Gland I = Optic Chiasm J = Sinus

Question 27

Describe the circulation of CSF?

Answer 27

1. Produced by the choroid plexus of both lateral ventricles 2. Passes into the third ventricle 3. Goes via the cerebral aqueduct into the fourth ventricle 4. Passes into subarachnoid space 5. Some goes into central canal of spinal cord 6. Most is reabsorbed from the subarachnoid space by the arachnoid granulations 7. Reabsorbed into the dural venous sinuses

Question 28

Describe how raised ICP is transmitted?

Answer 28

This is transmitted along the subarachnoid space of the optic nerve sheath

Question 29

Describe how raised ICP leads to swollen discs?

Answer 29

Raised ICP compresses the optic nerve It also compresses the central retinal artery and vein This leads to bulging, swollen discs

Question 30

Describe damage to CN III?

Answer 30

This is susceptible to damage (Eg: Compression) Leads to the eye being ‘down and out’ with a dilated pupil

Question 31

Oculomotor nerve damage causes the eye to be in what position?

Answer 31

Down Out Dilated pupil

Question 32

Describe herniation/raised ICP?

Answer 32

Raised ICP can compress/stretch oculomotor nerve if medial temporal lobe herniates through tentorial notch

Question 33

Describe damage to the trochlear nerve (CN IV)?

Answer 33

This has a long intracranial course and is susceptible to injury: - Stretching - Compression Results in superior oblique paralysis Eye cannot move inferior

Question 34

Describe damage to CN VI? (Abducens)

Answer 34

Long intracranial course and is susceptible to stretching Results in lateral rectus paralysis Eye cannot move laterally