Visual field defects Flashcards
visual field defects - types
- (right/left) anopia
- Bitemporal hemianopia
- (left/right) homonymous hemianopia
- (left/right) upper quadrantic anopia
- (left/right) lower quadrantic anopia
- (left/right) hemianopia with macular sparing
- Central scotoma
Central scotoma is caused by
macular degeneration
(right or left) anopia?
total blindness of left or right eye
(right or left) anopia - mechanism
complete lesion of the right or left optic nerve
bitemporal hemianopia?
vision is missing in the outer half of both the right and left visual field.
bitemporal hemianopia is caused by
pressure exerted on the optic chiasm by a pituitary tumor
(left or right) homonymous hemianopia is a
visual field loss on the left or right side of the vertical midline
(left or right) homonymous hemianopia is caused by
- a lesion in (left or right) of the left optic tract
2. a complete lesion in (left or right) of the left optic radiation
(left of right) hemianopia with macular sparing is caused by
posterior cerebral artery occlusion (Lesion of the occipital cortex)
left upper quadrantic anopia is caused by
- partial involvement of the optic radiation (Meyer loop) by a lesion in the right temporal lobe
- Middle cerebral artery stroke
Mayer loop contains fibers from the
inferior retina (superior part of the visual field)
Mayer loop pathway
through the temporal lobe by looping around the inferior horn of the lateral ventricle
left lower quadrantic anopia is caused by
- partial involvement of the optic radiation (dorsal optic radiation) by a lesion in the left parietal lobe
- Middle cerebral artery stroke
dorsal optic radiation
Fibers from the superior retina (inferior part of the visual field)
dorsal optic radiation - pathway
takes shortest path (through the parietal lobe) via internal capsule
Calcarine sulcus function
primary visual cortex (V1) is concentrated
medial longitudinal fasciculus (MLF) is a
pair of tracts that allows for crosstalk between CN VI and the contralateral CN III nuclei
medial longitudinal fasciculus (MLF) - function
it coordinates both eyes to move in same horizontal direction
medial longitudinal fasciculus (MLF) - speed of communication (and mechanism and why)
highly myelinated –> to communicate quickly so eyes move at the same time
medial longitudinal fasciculus (MLF) - highly myelinated
–>…
to communicate quickly so eyes move at the same time
bilateral medial longitudinal fasciculus (MLF) - classically seen in
multiple sclerosis
medial longitudinal fasciculus (MLF) - it coordinates both eyes to move in same horizontal direction - mechanism
when looking left, the left nucleus of CN VI fires, which contracts the left lateral rectus and stimulates the contralateral (right) nucleous of CN III (via the MLF) to contract the right medial rectus
lesion in medial longitudinal fasciculus (MLF) –>
internuclear ophthalmoplegia (INO)
internuclear ophthalmoplegia - mechanism
Lack of communication such that when CN VI nucleous activates ipsilateral lateral rectus, contralateral CN III nucleous does not stimulate medial rectus to fire, and the abducting eye gets nystagmous (CN VI overfires to stimulate III) –> the Convergense is normal
internuclear ophthalmoplegia - the abducting eye gets nystagmous - mechanism
CN VI overfires to stimulate CN III
directional term for internuclear ophthalmoplegia (e.g. right INO, left INO)
refers to which eye is paralysed
internuclear ophthalmoplegia - convergence?
normal
internuclear ophthalmoplegia usually implies
intrinsic brainstem disease
MCC of unilateral internuclear ophthalmoplegia
stroke
disease that can mimic a lesion of the medial longitudinal fasciculus
myasthenia gravis
