The eye & raised ICP Flashcards
What is raised ICP?
Increase in pressure within the cranial cavity caused by either an increased pressure in fluid surrounding the brain or an increase in pressure within the brain itself
Causes of raised ICP
Brain tumour Head injry Hydrocephalus (increased fluid around the brain) Meningitis Stroke
What 3 components make up the intracranial volume?
Brain
Blood
CSF
Why is increased ICP a serious medical problem?
Cranial cavity is an enclosed rigid space
Can’t cope with increase in pressure - causes damage to tissues, shifts in tissues, herniation and constriction of blood vessels
Eye related presentations of raised ICP
Transient blurred vision Double vision Loss of vision Papilloedema Pupillary changes
What percentage of patients with raised ICP report visual problems?
65-75%
What covers the optic nerves?
Dura mater
Arachnoid mater
Sub-arachnoid mater
Pia mater
What are meninges?
Protective covering of brain & spinal cord
What is the dura mater often called?
Hard/tough mother
What supplies the sensory innervation of the dura mater?
CN V
What is the arachnoid mater often called?
Spidery mother
What is found in the subarachnoid space?
Circulating CSF and blood vessels
What is the Pia Mater also know as?
Faithful mother
What does the Pia mater adhere to?
The brain (and vessels and nerves entering or leaving)
Where is CSF produced?
Choroid plexus of the ventricles
Where is CSF reabsorbed?
Dural venous sinuses
Where is a lumbar puncture taken to obtain a sample of CSF?
L3/4 or L4/5
Where does CSF end?
S2
Describe CSF circulation
Choroid plexus produces CSF
CSF passes into lateral ventricle
CSF then passes through intraventricular foramniae into 3rd ventricle
CSF then passes down the cerebral aqueduct (of sylvius) into 4th ventricle
Most CSF passes into subarachnoid space through apertures
Some CSF goes down the central canal of the spinal cord
Rebasorbed from the subarachnoid space via the arachnoid granulations into the drual venous sinuses
Why does raised ICP affect the eye?
Compresses optic nerve & the central artery and vein of the retina
Visual symptoms of raised ICP
Transient visual obscurations Transient flickering Blurring of vision Constriction of the visual field Decreased colour perception
What symptoms does compression of CN III cause?
Paralysis of somatic motor innervation (4 extraocular muscles & eyelid)
Paralysis of parasympathetic innervation sphincter
Slow light reflex
Eye tuned inferolaterally
Which cranial nerve is particularly susceptible to stretching and compression?
CN IV (long,thin)
What is the only nerve that comes out the posterior aspect of the brain?
CN IV
Which nerve damage causes diplopia going downstairs?
CN IV
Which is the abducent nerve susceptible to damage by stretching?
Long intracranial course
What is papilloedema?
Swelling of the disc due to raised ICP
What are the parts of a CN II examination?
Opthalmoscopy Visual acuity Pupil exam Visual field assessment Colour vision
Signs of raised ICP on ophthalmoscopy
Bilateral swollen discs
Vessels look toruous and engored
Pathophysiology of papilloedema
Subarachnoid space around CN II
When ICP rises this transmitted to SAS then onto CN II
Causes interuption of axoplasmic flow and venous congestion = swollen discs
What happens to the brain in raised ICP?
Brain is squeezed through foramen magnum, brainstem compressed
What other conditions can cause disc swelling?
Malignant hypertension
What are the functions of the CSF?
Maintains stable extracellular environment for the brain Buoyancy Provides echanical protection Waster removal Nutrition
What is the choroid plexus?
A network f capillaries which filter blood to form CSF
What physiological actions lead to increased ICP?
Obstruction to CSF circulation
Overproduction of CSF (e.g. by tumour)
Inadequate absorption
Patient with bilateral disc swelling, normal MRI, Lumbar puncture shows raised CSF opening pressure?
Idiopathic Intracranial Hypertension (IIH)
What happens if disc swelling becomes chronic?
Disc swelling subsides
Disk become atrophic & pale
Loss of visual function
Blindness may result
