Ophthalmology Flashcards
What is the optic chiasm?
The part of the brain where some of the optic nerves cross over as they go from the eyes to the brain
It is an X shape
Where is the optic chiasm?
It is at the bottom of the brain immediately below the hypothalamus
Which nerves cross over at the optic chiasm and which don’t?
The nerves coming from the nasal side of each retina cross over
The nerves coming from the temporal sides of the retina don’t
What is bitemporal hemianopia?
Partial blindness where there is loss of vision in the outer half of the right and left visual field
What causes bitemporal hemianopia?
A lesion or compression at optic chiasm
Affects the crossing over of the nasal retinae nerves
The visual impulse from both nasal retina are affected leading to inability to view the temporal vision
On which part of the retina does images from the temporal visual field fall?
On the nasal retinae
What are ‘incongruous field defects’?
Problems with vision that do not match up exactly between the two eyes
So more of the visual field is lost in one eye than the other
What would a lesion on the optic nerve (i.e. before the optic chiasm) cause?
Monocular visual loss
Describe the journey of a nerve impulse from the eyeball to the visual cortex?
R or L Eyeball
R or L Optic nerve
Optic chiasm:
- decussation of nasal retinal nerves
R or L Optic tract
R or L thalamus: lateral geniculate nucleus
R or L thalamus
What would a lesion on the optic chiasm cause?
Bitemporal hemianopia
Loss of vision in temporal fields
What does homonymous mean?
Same problem on both sides (eyes)
Homonymous = congruous
What does congruous mean?
Same problem on both sides (eyes)
Congruous = homonymous
What would a person with higher cortical visual dysfunction suffer with?
Difficulty describing pictures
Difficulty recognising faces
Difficulty drawing a clock
Which part of the thalamus is vision processed in?
Lateral geniculate nucleus
What is scotoma?
Area of partial alteration in the field of vision
Such as weird zigzags, blind spots etc.
What is papilloedema?
Swollen optic disc
When you look at someone’s eye using an ophthalmoscope it appears white and jagged in the centre
What is papilloedema a sign of?
Raised inter-cranial pressure
What is diplopia?
Double vision
What is cranial nerve III called?
Oculomotor
What does cranial nerve III do in terms of the eye?
Innervates the extra-ocular muscles
Controls:
- eyelid elevation
- elevation, depression, adduction of the eye
- pupillary constriction
- lens accommodation
What are the extra-ocular muscles?
Superior rectus
Lateral rectus
Medial rectus
Inferior rectus
Superior oblique
Inferior oblique
Which muscles move the eye up and down?
Superior and inferior rectus
Which muscles move the eye side to side?
Medial and lateral rectus
What does the superior oblique muscle do to the eye?
Internal rotation
Depression of eye
Abduction: lateral movement
Which nerve innervates the superior oblique muscle?
Trochlear (IV)
Which nerve innervates the inferior oblique muscle?
Oculomotor (III)
What does the inferior oblique muscle do to the eye?
External rotation
Elevation of eye
Adduction: medial movement
What is extorsion and intorsion?
Another name for the rotation of the eye internally or externally
Which eye muscles does the oculomotor nerve innervate?
Medial, inferior and superior rectus
Inferior oblique
What eye muscles does the trochlear nerve innervate?
Superior oblique
What eye muscles does the abducens nerve innervate?
Lateral rectus
Which nerve supplies the lateral rectus?
Abducens
Which nerve supplies the superior oblique?
Trochlear
What would happen to they eye if there were a lesion on the oculomotor nerve?
Lateral squint, eye shifts laterally because there is no medial rectus pulling it back
Ptosis due to loss of oculomotor control which elevates eyelid
What is ptosis?
Drooping of eyelid
What would happen to the eye if there were a lesion on the trochlear nerve?
Eye elevated due to loss of superior oblique muscle depressing the eye
Medial squint - eye shifts medially due to loss of superior oblique muscle to pull the eye back laterally
What would happen to the eye if there were a lesion on the abducens nerve?
Eye doesn’t move laterally
Medial squint since no lateral rectus to pull it back
What is a ‘palsy’?
Paralysis, weakening
What is nystagmus?
Rhythmic to and fro oscillations of the eyes
What causes nystagmus?
Can be congenital
Or acquired
- stroke
- MS
What does sympathetic nervous system do to the pupil?
Dilates pupil
What does parasympathetic nervous system do to the pupil?
Constricts pupil
What does a problem with:
- parasympathetic
- sympathetic
nervous systems cause in the pupils?
Parasympathetic problem = pupils will dilate
Sympathetic problem = pupils will constrict
What is a relative afferent pupillary defect?
One pupil contracts with light
One pupil dilates with light, vision is poorer in this eye
