The Retina and Central Visual Pathways Flashcards
Label the following fundoscopic image of the retina
What is the name given to the painless temporary loss of vision that is sometimes described as a “black curtain over vision”?
What can cause this?
Amaurosis Fugax
Occlusion of the central retinal artery or opthalmic artery
Draw a labelled diagram of the visual pathway including visual fields.
Nasal fields of vision are detected by which fibres?
Temporal fibres
Temporal fields of vision are detected by which fibres?
Nasal fibres
Superior fields are picked up by which fibres?
Inferior fibres
Inferior fields are picked up by which fibres?
Superior fibres
Superior radiations pass through which lobe of the brain?
Parietal lobe
Inferior radiations pass though which lobe of the brain?
Temporal lobe
Where is the primary visual cortex found?
Occipital lobe
With regard to nasal fibres, what is important about the optic chiasm?
The nasal fibres decussate there
Do temporal fibres run ipsilateral or contralateral?
Ipsilateral
The optic tract runs lateral to which structure?
Lateral Geniculate Nucleus
Visual field defects are named based on what?
They are named based on the area of visual loss and not the site of the lesion
A lesion before the optic chiasm will produce which type of visual field defect?
Give two examples
Unilateral, ipsilateral
e.g. central scotoma, monocular vision loss
A lesion at or after the optic chiasm will produce which type of visual field defect?
Give an example.
Bilateral
e.g. Bitemporal hemianopia (lesion at optic chiasm)
A lesion after the optic chiasm will produce which type of visual field defect?
Give examples.
Bilateral and contralateral
e.g. Contralateral homonymous hemianopia
Contralateral superior quadrantopia
Contralateral inferior quadrantopia
Contralateral homonymous hemianopia with macular sparing
What conditions might cause monocular blindness due to damage to the optic nerve?
(for both children and for middle aged individuals)
Children: Glioma or Retinoblastoma
Middle aged adults: Optic sheath meningiomas
Bitemporal hemianopia is also known as what?
Which conditions cause this visual field defect?
Tunnel vision
Anything causing enlargement of the pituitary gland or anterior communicating artery
In a left homonomous hemianopia, on which side will the patient have the lesion and where?
What is the most common cause of this visual field defect?
Right optic tract
Vascular changes (e.g. stroke)
Neoplasia and trauma can also cause this
Explain the anatomical basis behind macular sparing.
Occipital lobe has a duel blood supply
- Posterior cerebral artery
- Middle cerebral artery
In a stroke affecting the PCA, the MCA occipital pole will continue to supply and therefore spare macular function
Draw out the pupillary light reflex pathway for light entering the left eye. Label the CNs and nuclei involved.
Where does CN II (Optic nerve) synapse in the pupillary light reflex?
Which structure do neurones arising from here then go onto supply bilaterally?
In the pretectal area (nucleus)
Edinger Westphal nucleus
The accomodation reflex if required for what?
Near vision
Focusing on things close to us
What are the “three C’s” of the accomodation reflex?
Which muscles are each of these carried out by?
Convergence - medial rectus
Pupillary Constriction - constrictor pupillae
Convexity of the lens - ciliary muscle
Image analysis is required to complete the accomodation reflex, what structure is necessary in order to achieve this?
Cerebral cortex
Through what nucleus does the accomodation reflex travel to reach the visual cortex?
The lateral geniculate nucleus
In which part of the retina are cones particularly common?
The macula
Which part of the retina is rich in rods?
What is particularly special about rods?
Peripheral retina
They work well in low light (more sensitive at night)
Does the optic disc contain photoreceptors?
No, it represents the “blind spot”
The lateral genicular nucleus projects to which lobe?
Occipital lobe
A patient has a tumour arising from the right cavernous sinus and invading medially towards the optic chiasm. Which visual field defect might this result in?
Right nasal hemianopia
If the tumour erodes medially, it will destroy fibres from the temporal retina of the right eye which subserves the nasal field of the right eye.
Destruction of the optic tract is rare. What would nne the consequence of compression of the right optic tract?
Left homonymous hemianopia without macula sparing
-No macula sparing as that is a feature of vascular lesions of the occipital lobe
Homonymous superior qudrantanopia is most commonmly seen in lesions to which part of the visual pathway?
Meyer’s loop (inferior optic radiation)
This contains fibres from the contralateral superior quarter of the field.
“Pie in the sky” defect
Photoreceptor cells synapse with which retinal cell type predominantly?
Bipolar cells
Can be thought of as the first order sensory neurones of the visual system
Internuclear opthalmoplegia can be caused by damage to which pathway?
Medial longitudinal fasciculus
A trauma patient is found to have had a bleed in the region of the left thalamus, including the lateral geniculate nucleus. Which visual signs might they display?
Right homonymous hemianopia
- Input from the left optic tract*
- Information for the right half of the visual field*
Where is the tumour in the image located?
Side:
Lobe:
Side: Right
Lobe: Temporal
A 62 year old male with a lesion in the right temporal lobe presents with a left superior homonymous quadrantanopia or “pie in the sky” defect. Why? (3)
Left visual field subserved by the right hemisphere. (horizontal plane defect)
The upper halves of the visual fields is carried in the temporal lobes, specifically in Meyer’s loop. (vertical plane defect)
A right temporal lobe lesion can lead to a homomymous loss of left upper field.
