week 1 the eye and ICP Flashcards
what is raised Intracranial Pressure? what two types are there?
Increase in pressure within the cranial cavity
Chronic or acute
causes of RICP
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
what is the problem with RICP?
Serious medical problem
Can cause damage to the brain and the spinal cord
what is the The Monro-Kellie hypothesis ?
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
what visual problems to patients with RICP report?
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)
what are the optic nerves actually?
CNS tracts
Covered by meninges, Dura, Arachnoid, Pia
what is the Space between arachnoid and pia called? why is this relevant?
Sub-arachnoid space
Filled with Cerebrospinal Fluid (CSF)
what is the meninges?
Protective coverings of brain and spinal cord
what does the meninges consist of (superficial to deep)
dura mater, arachnoid mater, subarachnoid space, pia
describe the dura mater
“Hard mother”
Tough
Sensory supply from CN V
- Encloses dural venous sinuses
describe the arachnoid mater
“Spidery mother”
Arachnoid granulations
describe the subarachnoid space
Circulating CSF and blood vessels
describe the pia
“Faithful mother”
Adheres to brain (and vessels and nerves entering or leaving)
what does the Subarachnoid Space surround? what is its function?
completely surrounds both brain & spinal cord -
continuous
cushions and protects
Subarachnoid Space contains what?
Contains circulating cerebrospinal fluid (CSF)
where is CSF produced?
choroid plexus of the ventricles
where is CSF reabsorbed?
into the dural venous sinuses, via arachnoid granulations
how can the subarachnoid Space (and therefore CSF) be accessed?
via lumbar puncture at L3/4 or L4/5 IV disc levels [note:spinal cord ends L2 but dura continues until S2]
what are the ventricles of the brain? where are they?
2 lateral (within the left and right cerebral hemispheres),
3rd (in the midline within the diencephalon)
4th (between the cerebellum & pons)
how does CSF get from 3rd to 4th ventricle?
the cerebral aqueduct
describe the circulation of CSF
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.
how is the optic nerve affected by RICP?
Raised ICP will be transmitted along the subarachnoid space in the optic nerve sheath → compress CN 2 + central retinal artery and vein
how is the optic disc affected by RICP?
Can lead to bulging or swollen optic discs = Papilloedema
what visual symptoms arise from RICP?
- transient visual obscurations (graying-out of vision),
- transient flickering
- blurring of vision
- constriction of the visual field
- decreased colour perception
how is the oculomotor nerve susceptible to damage?
Compression
Tentorial herniation
what occurs is CN3 is damaged?
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’
what two CNs come off the midbrain?
CN3 and 4
what is CN 4
trochlear nerve
what is the course of CN 4? how is it susceptible to damage
Long intracranial course - comes off back of midbrain, swamps sides and comes forwards.
susepctible to damage by stretching or compression
what is see if CN 4 pathology?
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
what is CN 6? where does it come off? how can RICP damage it?
Abducent Nerve
comes off at junction between the pons and the medulla.
damaged by stetting
what is see if CN 6 pathology?
Paralysis of lateral rectus muscle
Eye cannot move laterally in horizontal plane: - Medial deviation of the eye
