Pratical 2 - station 2 - eye movements & visual field Flashcards
What is the inferior of the eyeball divided into and by what?
Anterior cavity and vitreous chamber
Divided by the lens
Where is the anterior cavity?
In front of the lens
What can the anterior cavity be divided into?
Anterior chamber and the posterior chamber
Where is the anterior chamber?
Lies behind the cornea and in front of the iris
Where is the posterior chamber?
Behind the iris and in front of the suspensory ligaments and lens
What is the purpose of the aqueous humour?
Maintains the shape of the eyeball and supplies oxygen and nutrients to the lens and the cornea
maintains intraocular pressure to maintain eyeball shape and prevent collapse
What produces the aqueous humour?
Epithelium over the ciliary body
Where does the aqueous humour flow?
Produced from epithelium over ciliary body, flows through pupillary opening into anterior chamber, drains into canals of schlemm where the iris meets the cornea
What are the canals of Schlemm and where are they?
Modified vein set
around rim of anterior chamber in the angle of the eye where iris meet cornea
How often is the aqueous humour replaced?
Every 3 hours
What does the vitreous body do?
vitreous body - jelly like substance
helping preserve shape of eyeball and maintain focussing precision
keeps retina applied to choroids so even surface is maintained for a sharp image
Where is the retina?
Between the choroid and the vitreous body
What is the function of the fluid of the vitreous body?
Phagocytes - remove debris so vitreal floaters don’t occur
What are vitreal floaters?
Specks or shadows that dart in and out visual field, harmless, more common in elderly
What are the 6 extra-ocular eye muscles innervated by?
Lateral rectus - abducens
Superior oblique - trochlear
MR, SR, IF, IO - oculomotor
What is the action of the medial rectus and lateral rectus?
Medial rectus - adducts the eyeball
lateral rectus - abducts the eyeball
What is the action of the superior and inferior recti muslces?
Elevate and depress the eyeball when it is abducted
What is the action of the superior and inferior oblique muscles?
Depress and elevate the eyeball when it is adducted.
How do the eyelids close? (which muscles, nerves and action)
levator palpebral muscle (CN III) relaxes orbicularis oculi (CN VII) contracts
What is the action of the levator palpebrae superioris and what happens to the eye if it is damaged?
Elevates superior eyelid
Ptosis - dropping of the eyelid
What is the action of the superior rectus, nerve innervates it, what happens to eye if damaged?
Intorsion - elevation and adduction
CN III
If damaged pupil down and out as unopposed action of lateral rectus and superior oblique
What is the action of the inferior rectus, nerve innervates it, what happens to eye if damaged?
Extorsion - depression and adduction
CN III
IIf damaged pupil down and out as unopposed action of lateral rectus and superior oblique
What is the action of the medial rectus, nerve innervates it, what happens to eye if damaged?
CN III
Adduction
If damaged pupil down and out as unopposed action of lateral rectus and superior oblique
What is the action of the inferior oblique, nerve innervates it, what happens to eye if damaged?
CN III
Extorsion - acts with superior rectus to allow elevation
If damaged pupil down and out as unopposed action of lateral rectus and superior oblique
What is the action of the superior oblique, nerve innervates it, what happens to eye if damaged?
CN IV
Intorsion - acts with inferior rectus to allow depression
If damaged get weak downward eye movements so affected eye drifts upwards relative to normal eye as unopposed action of other extra-ocular muscles
What is the action of the lateral rectus, nerve innervates it, what happens to eye if damaged?
CN VI
Abduction
If damaged pupil is adducted as unopposed action of medial rectus
What is intorsion and extorsion and why do they occur?
Up and in, down and in
Superior and inferior rectus muscles don’t pull directly parallel to axis of eyeball so will pull pupil medially.
What are the 4 major pathological conditions which affect the eye?
Cataracts
Detached retina
Glaucoma
Pappiloedema
What are cataracts? Cause?
Opaqueness of the lens Cloudiness of the lens Congenital defects Persistent exposure to UV aging
How does a detached retina occur? Why is it bad?
Neural retina torn from pigment epithelium as mechanically unstable
Photoreceptors metabolically dependent on pigment contact so must be repaired
How does surgical repair of detached retina help?
Prevents further increase in detachment area but detached area won’t regain function
What is glaucoma? How does it occur?
Most common cause of blindness
Aqueous humour build up in anterior eye chamber as canal of Schlemm (scleral venous sinus) blocked
Effects of glaucoma
Causes intraocular pressure to increase and fluid compresses on lens into vitreous humour so retinal neurons and blood supply compressed producing ischaemia
Mild to irreversible visual impairment from persistent pressure
What is papilloedema?
Swelling of the optic disc (papilla) as increased CSF pressure and raised intracranial pressure slowing venous return from retina as compresses on optic nerve and vessels
What is papilloedema a sign of?
Raised intracranial pressure - seen in neurological examination of eye and is bilateral
What is the effect of papilloedema?
if left untreated pressure increases so constricts retinal ganglion cell axons so can lead to blindness
Swelling at constriction leads to disk margin becoming blurred and optic cup lost
Papilla may protrude into eye if papilla pressure increases
Which structure is immediately posterior to the optic chiasm?
Pituitary gland
Which bone is the optic canal found in?
Sphenoid bone
Where do the axons from the back of the eyeball cross?
X shaped optic chiasm
What fibres do optic tracts contain?
From lateral (temporal) retina of eye on the same side and nasal retina from opposite side (all info. from same half of visual field)
Where do the paired optic tracts send axons?
Sweep posteriorly and send axons to synapse in the lateral geniculate nucleus of the thalamus
Where do the axons project form the lateral geniculate nucleus of the thalamus?
Through the internal capsule to form the optic radiations and project to the primary visual cortex in the occipital lobe
What happens in the primary visual cortex?
Conscious perception of visual images
What is the superior colliculus?
Visual reflex centre controlling extrinsic eye muscles
some fibres from optic tracts sent here
What is the pretectal nuclei?
Mediates papillary light reflexes
some fibres from optic tracts sent here
What field defect is there if there is a lesion to the partial optic nerve?
Ipsilateral scotoma
What field defect is there if there is a lesion to the complete optic nerve?
Monocular blindness in that eye
What field defect is there if there is a lesion to the optic chiasm?
Bitemporal hemianopia
What field defect is there if there is a lesion to the optic tract?
Homonymous hemianopia
What field defect is there if there is a lesion to the Meyer’s loop?
Homonymous upper quadrantanopia
What field defect is there if there is a lesion to the optic radiation?
Homonymous hemianopia
What field defect is there if there is a lesion to the visual cortex (medial)?
Homonymous hemianopia
What field defect is there if there is a lesion to the visual cortex (lateral-macular)?
Bilateral central scotoma
Define hemianopia?
Blindness over half the field of vision
