Flashcards in Eye and Raised Intracranial Pressure Deck (46):
What are the two humours of the eye and where are they located?
Aqueous humour = Anterior to lens
Vitreous humour = Posterior chamber
Where are the anterior and posterior chambers of the eye?
Anterior to the lens
Ant = in front of iris
Post = behind iris
What is the pathway of aqueous humour movement?
Produced in posterior chamber
Passes out and round the iris
Into anterior chamber
What might occur as a result of blockage of the aqueous humour pathway?
Increased pressure in anterior an posterior chamber
What might cause raise intracranial pressure?
Space occupying lesion, tumour, abscess or haemorrhage
What are the three main contents of the cranial cavity?
What is the Munro-Kellie Hypothesis?
An increase in volume of any of the brain cavity content must lead to a decrease in another (relationship between intracranial components and pressure)
If not relieved, what is the result of raised intracranial pressure?
What is hydrocephalus?
Water on the brain
CSF volume enlarges, ventricles enlarge, brain matter gives way
Why can an infant's brain increase in size with hydrocephalus, whereas an adults cannot?
Sutures in the child's cranial cavity have yet to fuse
Ability for growth and expansion
What is the sunset sign in hydrocephalus?
Sight of whites of the eye above the iris
What are meninges?
Membranes around the brain
What are the three layers surrounding the brain, and the spaces in between them?
What is the composition of the dura mater?
Hard, fibrous membrane
Endoesteal layer (stuck to inside of cranial cavity)
What is the composition of the arachnoid mater?
Spiders web like composition
What is contained in the subarachnoid space?
What is the composition of the pia mater?
Thin layer (one cell thick)
Surrounds brain (follows the gyri and sulci)
What is the falx cerebri?
Extension of dura mater
Separates the two cerebral hemispheres
What is the tentorium cerebelli?
Extension of dura mater
Separates cerebellum form cerebral hemispheres
What is the falx cerebelli?
Extension of dura mater
Separates the two hemispheres of the cerebellum
What is the tentorial notch?
Mid brain passes through here
What is the infundibulum of hypophysis cerebri?
Stalk of the pituitary
What is diaphragma sellae?
Part of dura mater where pituitary sits
Where are veins of the brain located?
What are the dural venous sinuses?
Spaces between the folds of the dura mater containing venous blood (histologically, NOT veins)
What re the components of the lateral ventricles?
Frontal (anterior) horns
Occipital (posterior) horns
Temporal (inferior) horns
Where is the third ventricle located?
Where is the fourth ventricle located?
Between pons/medulla and cerebellum
What connects the lateral ventricles to the third ventricle?
What connects the third ventricle to the fourth ventricle?
What is the route of CSF circulation?
Chroroid plexus (production in all ventricles!)
Two lateral ventricles
Median aperture/two lateral apertures (or central canal of spinal cord)
Superior sagittal sinus
Reabsorption into venous system
What visual problems can result form raised intracranial pressure?
Transient blurred vision
Loss of vision
Compression of which CN may lead to diplopia?
CN III, IV or VI
How may diplopia due to raised ICP present?
Will be worse when looking in direction of affected muscle
E.g. compression of CN IV affects superior oblique -> diplopia worse on looking down and out
Compression of which CN may lead to a dilated pupil, and how?
Parasympathetic supply to sphincter pupillae compromised
Unopposed sympathetic stimulation of dilator pupillae
What is an early sign of raised intracranial pressure?
Fixed, dilated pupil
Why is the optic nerve different to other cranial nerves?
It is an extension of the CNS tract
What covers the optic nerve?
Meninges (dura, arachnoid and pia mater)
What affect does raised ICP have on the optic nerve?
Raised ICP = raised pressure in subarachnoid space
Transmitted along length of optic nerve
Compresses optic nerve, central artery and vein of retina
What are the consequences of raised ICP on the optic nerve?
Papilloedema (bulging/swollen discs)
Transient visual obsurations
Blurring of vision
Constriction of the visual field
Decreased colour perception
What are the possible outcomes of damage to CN III?
Paralysis of somatic motor innervation (4 extra ocular muscles and eyelid)
Paralysis of parasympathetic innervation of sphincter pupillae
Lose/slowness of pupillary light reflex, dilated pupil, ptosis, eye turned inferolaterally
What are the possible outcomes of damage to CN IV?
Paralysis of superior oblique (so inferior oblique is unopposed)
Eye cant move inferomedially
Diplopia when looking down
What are the possible outcomes of damage to CN VI?
Paralysis of lateral rectus
Eye cannot move laterally in horizontal plane
In which ways is CN III susceptible to damage?
In which ways is CN IV susceptible to damage?