B7.032 Prework 1: Visual System

Question 1

2 neuron optic system

Answer 1

1. ganglion cells

2. lateral geniculate body

Question 2

what happens in the optic chiasm

Answer 2

fibers sub serving temporal fields (nasal retina) cross

Question 3

course of the optic tract

Answer 3

from chiasm, around midbrain to:
primarily LGN
reflex fibers to superior colliculus
pretectal area

Question 4

outflow from LGN

Answer 4

2 groups of visual radiations
upper, parietal loop to upper bank of calcarine fissure
lower, temporal (Meyer’s) loop to lower bank of calcarine fissure

Question 5

where is the primary visual cortex

Answer 5

around the calcarine fissure in the occipital lobe

Question 6

size of visual fields

Answer 6

about 180 deg

130 deg of which overlaps between right and left eye

Question 7

what is the physiological blind spot

Answer 7

optic nerve head in the back of the retina that doesn’t contain photoreceptors
filled in by the brain

Question 8

how are images projected onto the retina

Answer 8

upside down and backward

Question 9

left visual field

Answer 9

right occipital cortex

Question 10

right visual field

Answer 10

left occipital cortex

Question 11

nasal retinal fibers

Answer 11

temporal fields

crossed

Question 12

temporal retinal fibers

Answer 12

nasal fields

uncrossed

Question 13

central vision

Answer 13

higher level of acuity

posterior occipital cortex

Question 14

peripheral vision

Answer 14

lower level of acuity

anterior occipital cortex

Question 15

upper visual field

Answer 15

to inferior occipital cortex via Meyer’s loop

Question 16

inferior visual field

Answer 16

to superior occipital cortex via parietal loops

Question 17

monocular visual defect

Answer 17

lesion anterior to chiasm

optic nerve or eye itself

Question 18

bitemporal hemianopia

Answer 18

temporal fields blacked out

lesion within chiasm where temporal field fibers cross

Question 19

binasal hemianopia

Answer 19

nasal fields blacked out

lesion compressing optic chiasm from the lateral sides

Question 20

homonymous hemianopia

Answer 20

same side field blacked out in both eyes
retro-chiasmic lesion (optic tract / visual radiations / occipital lobe)
cannot localize further without looking at other systems

Question 21

upper quadrantanopia

Answer 21

same side upper quadrant blacked out in both eyes

temporal lobe lesion affecting Meyer’s loop

Question 22

lower quadrantanopia

Answer 22

same side lower quadrant blacked out in both eyes

parietal lobe lesion affecting upper visual radiations

Question 23

homonymous hemianopia with macular sparing

Answer 23

same side field blacked out in both eyes, with central vision preserved
hallmark of stroke / blood supply issue

Question 24

blood supply of the optic tract

Answer 24

PCA is anterior
MCA is posterior
if PCA is occluded, MCA provides alternative blood supply to posterior occipital cortex, sparing the macula

Question 25

congruity

Answer 25

visual information from the same field of different eyes becomes co-registered the further position in the visual system

• lesion close to eye = incongruous
• lesion close to cortex = congruous

Question 26

complete visual loss

Answer 26

full chiasm knocked out
entire occipital lobe knocked out
occlusion of top of basilar (but will have macular sparing)

Question 27

diagnostic tools to assess vision

Answer 27

Snellen chart
glasses
pinhole
something red
flashlight
visual field testing (confrontation, Humphrey fields)
opthalmoscope

Question 28

visual acuity

Answer 28

smallest size that can be reliably identified

i.e. 20/20 vision

Question 29

pin hole

Answer 29

eliminates refractive error

no need for focusing

Question 30

function of the swinging flashlight test

Answer 30

assess for an afferent pupillary defect (marcus gunn pupil)

Question 31

what is an afferent pupillary defect

Answer 31

pupil gets bigger when shining light in one eye over the other
suggestive of subtle optic nerve lesion (optic neuropathy)

Question 32

color desaturation

Answer 32

color looks darker in an eye with optic neuropathy