Week 6 Flashcards
Briefly outline the visual pathway from eyes to brain
Eyes → optic nerves → optic chiasm → optic tracts → optic radiations
Where are images of the right external environment relayed to?
Left side of the back of the eye
What is the result of optic nerve damage?
Loss of vision in that eye
What is the result of optic chiasm damage?
Crossing fibres are affected which causes loss of outer part of visual field of each eye
What could be the cause of optic chiasm damage?
Pituitary tumour compressing the chiasm
What is the result of optic radiation or cortical damage?
Loss of vision on opposite side to lesion
What does the red test look for?
Relative field defect
What does the finger movement test look for?
Absolute field defect
What is hemianopia?
Loss of vision on one side
What can cause hemianopia?
Ischaemia due to blockage of posterior or middle cerebral artery
What does homonymous mean?
Of the same distribution on both sides
What are the signs of homonymous hemianopia?
Complaint of poor vision with normal visual acuity
Bumping into objects
Stroke with movement problems on one side
What is the normal pupil response to light?
Rapid constriction of pupil to light (direct) and simultaneous constriction of other pupil (consensual)
Briefly outline the pathway of the pupil response
Light shone in one eye → signal passed down optic nerve → splits in chiasm → passes down both sides to upper tectal region of midbrain → passed to CN 3 on both sides → causes constriction of both pupils
What part of the visual pathway is affected by optic nerve, optic chiasm and optic radiations damage?
Nerve - clarity, pupil
Chiasm - visual fields
Radiations - homonymous
What part of the brain receives visual information?
Primary visual cortex/V1/striate cortex
How does light interact with the retina?
Deepest layers of retina (photoreceptors) receive light first; back-to-front mechanism
Approximately how long is the optic nerve?
50mm
How many optic fibres decussate at the optic chiasm?
50-60%
What is the LGN?
Lateral geniculate nucleus
Relay centre of the thalamus, alternating white and grey matter, 6 layers
What is the superior colliculus?
Area of the midbrain involved in control of eye movement to track a moving stimulus
Where is the pituitary stalk in relation to the optic chiasm?
Underneath
Where can optic fibres project?
LGN
Superior colliculus
Pretectal area
Input to which part of the retina will always cross over?
Nasal retina
What defect results from a partial optic nerve lesion?
Ipsilateral scotoma
What defect results from a complete optic nerve lesion?
Blindness in that eye
What defect results from an optic chiasm lesion?
Bitemporal hemianopia
What defect results from an optic tract lesion?
Homonymous hemianopia
What defect results from a Meyer’s loop lesion?
Homonymous upper quadrantanopia
What is Meyer’s loop?
Part of the optic radiation which sweeps back on itself into the temporal lobe, just lateral to the temporal horn of the lateral ventricle
What defect results from an optic radiation lesion?
Homonymous hemianopia
What defect results from a visual cortex lesion?
Homonymous hemianopia
What defect results from a bilateral macular cortex lesion?
Bilateral central scotoma
What can cause optic nerve lesions?
Acute optic neuritis
Multiple sclerosis
Indirect traumatic optic neuropathy
Optic atrophy
What can cause optic chiasm lesions?
Tumours (pituitary adenoma, meningioma)
Aneurysms (ACA)
What can cause optic tract lesions?
Tumours
Trauma
Aneurysm of posterior cerebral artery
What is Goldmann perimetry?
Assesses the extent of visual field
A test light is used as the stimulus (kinetic or static) and visual field can be mapped according to detection of the light
What is the pupillary light reflex?
Pupil constriction in response to light
What is the accommodation reflex?
Pupil constriction and convergence of the eyes when looking from a distant object to a close one
Is pupil constriction under sympathetic or parasympathetic control?
Parasympathetic
What is the pathway for pupil constriction?
Edinger-Westphal nucleus → ciliary ganglion → eye
What is the pathway for pupil dilation?
Spinal cord → superior cervical ganglion → eye
Is pupil dilation under sympathetic or parasympathetic control?
Sympathetic
What nerves are involved in the afferent and efferent pathway of the pupillary light reflex?
Afferent - optic nerve
Efferent - occulomotor
Briefly outline the pathway of the pupillary light reflex
Light shone in right eye → information from right eye reaches pretectal nuclei on right and left → both Eddinger-Westphal nuclei activated → right and left oculomotor nerves activated → constriction of both pupils
What is hippus and when might it be seen?
Initial dilation/oscillation in response to light which is normal and can be found in some healthy young people
What is the swinging flashlight test?
Test to identify asymmetry of afferent input in the pupillary light reflex (called a relative afferent pupil defect (RAPD))
What can cause a RAPD?
Optic neuritis
Large retinal detachment
What would be seen in an abnormal swinging flashlight test?
When moving the light source from the right to left eye, the left eye paradoxically dilates (problem with left eye afferent limb)
What are the 3 components of the accommodation-convergence reflex and what muscles are responsible for each?
Pupil constriction (constrictor pupillae) Lens accommodation (ciliary muscles) Convergence of eyes (medial rectus muscles)
What is the stimulus in the accommodation-convergence reflex test?
Out-of-focus image
What nerves constitute the afferent and efferent limbs of the accommodation-convergence reflex?
Afferent - optic nerve
Efferent - oculomotor nerve
How are the pupils clinically examined?
- Inspect (irregularity/asymmetry)
- Direct and consensual light response
- Swinging light test
- Accommodation-convergence reflex test
What is the Edinger-Westphal nucleus?
Accessory oculomotor nucleus
Parasympathetic pre-ganglionic nucleus that innervates the iris sphincter muscle and the ciliary muscle
What is the calcarine sulcus a landmark for?
Marks primary visual cortex within the superior and inferior calcarine gyri
What is the superior colliculus also known as?
Tectum
What cranial nerves pass through the venous cavernous sinus?
Oculomotor
Trochlear
Abducens
What percentage of brain tumours are anaplastic astrocytomas?
80%
What cranial nerve is affected by suprasellar meningioma?
Oculomotor nerve
What signs indicate that the oculomotor nerve has been compromised?
Fixed and dilated pupil
What epithelium lines the air sinuses of the skull?
Respiratory epithelium
What mneumoic can be used to determine what cranial nerves are sensory and/or motor in order?
Small ships make money but my brother says big boats make more
What piece of equipment is required for a fundoscopy?
Ophthalmoscope
What is the red reflex?
Reddish-orange reflection of light from the back of the eye observed when using an ophthalmoscope
What vascular arcades are found in the eye?
Retinal - superior and inferior
How can veins and arteries in the eye be distinguished?
Arteries - thin and bright
Veins - thick and dark
How would you check the macula during a fundoscopy?
Ask the patient to look directly into the light
How are facial injuries classified?
Le Fort I (lower)
Le Fort II (middle)
Le Fort III (upper)
What Le Fort classifications are associated with base of skull fractures?
II and III
How might surgeons use hyaluronic acid?
Lip fillers
Scar reduction
