Retrochiasmal Disorders Flashcards
Retrochiasmal anatomy
Optic tract
LGN
Optic radiations
Striate cortex/primary visualcortex/B17
Blood supply to the optic tract
Anterior choroidal artery
Posterior communicating artery
Optic tract lesion
- incongruous contralateral homonymous hemianopsia
- acuity is usually preserved
- a homonymous hemianopsia accompanied by normal VA but a positive RAPD ipsilateral to the field defect is highly suggestive of an optic tract disturbance
- with isolated optic tract lesion, patient may have bilateral optic atrophy with ipsilateral temporal pallor and contralateral band atrophy
Object located in the left hemifield of each eye goes to the _____LGM
Right
LGN layers 1,4,6
layer 1,4,6 receives fibers from contralateral eye (left eye) nasal retina
LGN layers 2,3,5
Receives fibers from ipsilateral eye (right eye) temporal retina
Magnocellular layers of LGN
Layers 1,2 (bottom layers)
Parvocellular layers in LGN
3,4,5,6 (top 4 layers)
LGN lesion
- A horizontal homonymous sectoranopia is the hallmark of posterior choroidal artery territory infarction
- mirror image field defect (an upper nad lower homonymous sectoranopsia) due to anteiror choroidal artery infarction
Optic radiation
Inferior retina=course anteirorly and temporally and make the Meyer’s loop (temporal)
Superior retina fibers=course superiority into the partial lobe
PITS
-in regards to retinal fibers, not VF
Blood supply for the optic radiation
MCA is the major vessel to the optic radiations
Can get some from posterior choroidal artery as well
Optic radiation lesion
- Incongruous contralteral homonymous hemianopsia denser superiorly (pie in the sky) due to an isolated lesion of Meyer’s loop
- dense contralateral homonymous hemianopsia due to complete interruption of the optic radiations
- VA is spared in unilateral lesions, but can be impaired if bilateral lesion are present
Most common cause of optic radiation hemianopsia in adutls
Strokes in the MCA distribution and neoplasms are the most common
Visual cortex anatomy
Occipital lobe
Calcarine fissure
-divides into superior and inferior zone
Layer 3 of visual cortex
Sends taxons to other cortical layers
Layer 4 of visual cortex
Receives the primary input from the LGN. Activity of V1 cells depends entirely on LGN inputs
Layers 5 and 6 of visual cortex
Sends axons to subcortical areas. Layer 6 also provides direct feedback to the LGN
Left visual hemifield and visual cortex
It is demonstrated with the corresponding right calcarine fissure opened to reveal the fissure base and calcarine banks. The vertical hemianopic meridian is represented along the boarders of the calcarine lips. The lower vertical meridian of the visual field, line AD, is represented along the perimeter of upper striate cortex. The upper vertical meridian of the visual field is similarly represented along the border of the lower calcarine lip
Surface are of the striate cortex
Appx 55-60% of the surface are located posteriorly is responsible for the central 10 degrees of vision. The anteiror striate cortex subserved the temporal 30 degrees of the VF of the contralateral eye
Blood supply to the visual cortex
PCA
Occipital lobe lesions: macualr sparing
- contralateral congruous homonymous hemianopsia respecting the vertical meridian
- macular sparing ‘
- due to PCA stroke
- macular can get blood supply from the MCA so it gets spared
Unilateral occipital lobe tip disturbance
Contralteral homonymous hemianopic/quadrantic central scotomas are a sign
-usually from trauam, usually not infarct
Occipital lobe lesion with sparing or involvement of the tmperoal crescent
Sparing or invovlemtn of the temporal crescent. If an occipital lobe lesion does not involve the anterior striate cortex, the temporal 30 degrees of the VF of the contralateral eye may be spared
Key hole VF in occipital lobe lesion
Keyhole residual visual field (macular sparing hemianopsias) due to bialteral PCA infarction
-step off VF: sparing of central vision is greater in the right visual field than the left, and the demarcation between the two respects the vertical meridian
