Retrochiasmal Disorders

Question 1

Retrochiasmal anatomy

Answer 1

Optic tract
LGN
Optic radiations
Striate cortex/primary visualcortex/B17

Question 2

Blood supply to the optic tract

Answer 2

Anterior choroidal artery

Posterior communicating artery

Question 3

Optic tract lesion

Answer 3

• 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

Question 4

Object located in the left hemifield of each eye goes to the _____LGM

Answer 4

Right

Question 5

LGN layers 1,4,6

Answer 5

layer 1,4,6 receives fibers from contralateral eye (left eye) nasal retina

Question 6

LGN layers 2,3,5

Answer 6

Receives fibers from ipsilateral eye (right eye) temporal retina

Question 7

Magnocellular layers of LGN

Answer 7

Layers 1,2 (bottom layers)

Question 8

Parvocellular layers in LGN

Answer 8

3,4,5,6 (top 4 layers)

Question 9

LGN lesion

Answer 9

• 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

Question 10

Optic radiation

Answer 10

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

Question 11

Blood supply for the optic radiation

Answer 11

MCA is the major vessel to the optic radiations

Can get some from posterior choroidal artery as well

Question 12

Optic radiation lesion

Answer 12

• 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

Question 13

Most common cause of optic radiation hemianopsia in adutls

Answer 13

Strokes in the MCA distribution and neoplasms are the most common

Question 14

Visual cortex anatomy

Answer 14

Occipital lobe
Calcarine fissure
-divides into superior and inferior zone

Question 15

Layer 3 of visual cortex

Answer 15

Sends taxons to other cortical layers

Question 16

Layer 4 of visual cortex

Answer 16

Receives the primary input from the LGN. Activity of V1 cells depends entirely on LGN inputs

Question 17

Layers 5 and 6 of visual cortex

Answer 17

Sends axons to subcortical areas. Layer 6 also provides direct feedback to the LGN

Question 18

Left visual hemifield and visual cortex

Answer 18

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

Question 19

Surface are of the striate cortex

Answer 19

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

Question 20

Blood supply to the visual cortex

Answer 20

PCA

Question 21

Occipital lobe lesions: macualr sparing

Answer 21

• 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

Question 22

Unilateral occipital lobe tip disturbance

Answer 22

Contralteral homonymous hemianopic/quadrantic central scotomas are a sign
-usually from trauam, usually not infarct

Question 23

Occipital lobe lesion with sparing or involvement of the tmperoal crescent

Answer 23

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

Question 24

Key hole VF in occipital lobe lesion

Answer 24

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

Question 25

Occipital lobe lesion: quadrantic field defects

Answer 25

Due to restricted lesion of the upper or lower bands of the calcarine cortex

Question 26

Occipital lobe lesions: bialteral altitudinal hemianopsia

Answer 26

Respect the horizontal meridian due to bilateral upper and lower bank disturbances

Question 27

If there is a VF defect that respects the horizontal midline and is unilateral, what is first thought

Answer 27

Ischemia (maybe of ONH?)

Question 28

Most common cause of occipital lobe lesions in adults

Answer 28

PCA stroke