Retinotopic organisation Flashcards
What helps informed our understanding of position along the visual pathway of fibres that originate from various points on the retina?
neurobiological research in primates and non-primates and observations of visual dysfunction or abnormalities in human subjects by neuro-ophthalmologists
What type of visual defect would damage to the L optic nerve cause?
blindness in L eye
What is an example of pathology that could cause damage to the L optic nerve?
aneurysm in ophthalmic artery
What type of visual defect would be caused by pathology at the L side of the optic chiasma?
incongruous ipsilateral (L) nasal hemianopia
What is an example of a lesion that could cause an incongruous ipsilateral nasal hemianopia (causing lesion to L side of optic chiasma)?
aneurysm of terminal portion of the internal carotid artery
What is shown in the radiogaphic image?
digitally subtracted arterial phase of a carotid arteriogram of a 48-year-old patient suffering incongruous ipsilateral nasal hemianopia caused by such an aneurysm (arrow).
What type of visual field defect will be seen in damage to the nasal retinal fibres decussating in the optic chiasma?
contralateral bitemporal homonymous heimanopia
What is a common cause of pathology to nasal retinal fibres decussating in the optic chiasma?
pituitary tumours
What is shown in the radiographic image?
coronal MR image of the sellar region in a 31-year-old patient who presented with bitemporal hemianopia. A large pituitary tumour can be seen compressing the optic chiasma (C). ICA, Internal carotid artery; S, sphenoid sinus.
What type of visual field defect will be caused by a lesion to the left optic tract?
Contralateral (R) homoymous hemianopia
Why does a L optic tract lesion cause a R homonymous hemianopia?
damages uncrossed fibres from the temporal retina of the L eye and crossed fibres from nasal retina of R eye, therefore causes disturbances in R visual field
What is an example of a cause of a lesion to the optic tract?
vascular disturbances, such as occlusion of anterior choroidal artery
What type of visual field defect will be seen in a lesion in the temporal lobe affecting fibres furthest into the optic radiation?
contralateral homnymous superior quadrantanopia
(remember PITS - parietal=inferior, temporal=superior)
aka pie in the sky defect
Why does a lesion in the temporal lobe affecting fibres furthest into the optic radiation cause a contralateral homonymous superior quadrantanopia?
the fibres in the teporal lobe that are the furthest into the optic radiation are derived from the inferior retinal quadrants and therefore cause deficits in the superior visual field
What is an example of pathology which can cause optic radiation damage in the temporal lobe?
right MCA stroke
What is shown in the radiographic image?
Top: brain of 68-year-old with a stroke in the right middle cerebral artery (MCA) territory. Axial MR scan (diffusion weighted) shows size and limits of the right temporoparietal infarct (arrow).
Bottom: digital subtraction carotid arteriogram (anteroposterior projection) shows the aneurysm (arrow) at the bifurcation of the right MCA.
What type of visual field defects will be seen due to lesions affecting portions of the occipital cortex?
contralateral homonumous hemianopia with macula sparing
What is shown in the radiographic image?
MRI scan showing bilateral occipital cortical infarcts causing bilateral cortical blindness
