Central Visual Pathways and the Perceived Visual Field

Question 1

why is visual assessment limited in veterinary speices and what are the methods of assessing

Answer 1

because of interence of behaviour

1. observation, unfamiliar environment
2. ability to track (silent movement, ex. cotton balls)
3. visual placing (if small animal)
4. menace response (other reasons for failure)

Question 2

what is the visual pathway

Answer 2

1. retina
2. optic nerve
3. optic chiasm
4. optic tract
5. lateral geniculate nucleus
6. optic radiation
7. occipital cortex

Question 3

what is the visual field

Answer 3

total area in whcih objects can be seen in the peripheral vision as you focus your eyes on a central point

ex. predator –> more forward vision

prey –> more vision towards behind

Question 4

what is the pathway in the pupillary light relfex (PLR)

Answer 4

1. retina
2. optic nerve (CNII) –> afferent
3. optic chiasm
4. optic tract
5. pretectal nucleus
6. parasympathetic nucleus of CNIII –> efferent
7. bilateral pupil constriction

Question 5

what is the menace response pathway

Answer 5

1. retina
2. optic nerve (CNII) –> afferent
3. optic chiasm
4. optic tract
5. lateral geniculate nucleus
6. optic cortex
7. motor cortex
8. pontine nucleus
9. cerebellum
10. facial nerve nuclei (CNVII) –> efferent

Question 6

what is central (cortical) blindness

Answer 6

amaurosis

blindness without apparent lesion of the eyes

involves processing system

Question 7

where is the lesions in central (cortical) blindness

Answer 7

1. lateral geniculate nucleus
2. optic radiation
3. occipital cortex

Question 8

what are the clinical signs of central (cortical) blindness

Answer 8

normal PLR

absent menace response

blind

Question 9

what is peripheral (subcortical) blindness

Answer 9

involves collection/distribution system

Question 10

what are the lesions of peripheral (subcortical) blindness

Answer 10

1. eye
2. optic nerves
3. optic chiasm
4. optic tract

Question 11

what are the clinical signs of peripheral (subcortical) blindness

Answer 11

1. absent PLR
2. absent menace
3. blind

Question 12

what is the pathway of the dazzle reflex

Answer 12

1. retina
2. optic nerve (CNII) –> afferent
3. optic chiasm
4. optic tract
5. pretectal nucleus
6. facial nerve nuclei (CNVII) –> efferent
7. bilateral blinking

Question 13

what is the innervation of the extraocular muscles

Answer 13

1. dorsal rectus –> CN III
2. dorsal oblique –> CN IV - trochlear
3. medial rectus –> CN III
4. ventral oblique –> CN III
5. ventral rectus –> CN III
6. lateral rectus –> CN VI - abducens

Question 14

what are the functional classifications of cranial nerve III (occulomotor)

Answer 14

GSE: dorsal rectus, medual rectus, ventral rectus, ventral oblique, levator plapebrae

GVE: parasympathetic for pupil

Question 15

what are the functional classifications of cranial nerve IV (trochlear)

Answer 15

GSE: dorsal oblique

Question 16

what are the functional classifications of cranial nerve VI (abducent)

Answer 16

GSE: lateral rectus

retractor bulbi muscle in the eye

Question 17

what is strabismus

Answer 17

cross eyed

lateral or medial

Question 18

what causes lateral strabismus

Answer 18

cranial nerve II affected

Question 19

what causes medial strabismus

Answer 19

cranial nerve VI

Question 20

what causes strabismus in both eyes

Answer 20

cranial nerve IV

Question 21

what causes lateral strabismus and dilated pupil

Answer 21

CN III occulomotor nerve

dilated pupil because CN III innervates pupil

Question 22

what is eye position controlled by

Answer 22

the vestibular system