Chapter 8: Visual Pathways

Question 1

Can vitamin A be synthesized by humans?

Answer 1

no

Question 2

Describe the route traveled of the pupillary light reflex pathway of the afferent limb CN II?

Answer 2

• Light stimulates ganglion retinal cells > impulses travel up CN II which projects bilaterally to the pretectal nuclei (midbrain)
• pretectal nucleus projects bilaterally > Edinger- Westphal nuclei (CN III))

Question 3

Describe the efferent limb of the pupillary light reflex pathway.

Answer 3

Edinger Westphal nucleus (preganglionic parasympathetic) > ciliary ganglion (postganglionic parasympathetic) > pupillary sphincter muscle > miosis

Question 4

M3 activation of the ciliary muscle causes what actions?

Answer 4

contraction > accommodation for near vision

Question 5

M3 blockade causing blockage of ciliary muscle activation leads to what actions?

Answer 5

relaxation > focus for far vision

Question 6

What 3 events occur when an individual focuses on a nearby object

Answer 6

1. accommodation
2. convergence
3. pupillary constriction (miosis)

Question 7

Describe how accomodation takes place?

Answer 7

parasympathetic fibers contract the ciliary muscle, which relaxes suspensory ligaments, allowing the lens to increase its convexity (becoming more round). This increases refractive index of lens thereby focusing nearby object

Question 8

Describe how convergence takes place?

Answer 8

both medial rectus muscle contract adducting both eyes.

Question 9

A term used in general to describe Argyll Robertson pupil?

Answer 9

pupillary light-near dissociation

Question 10

What are conditions in which Argyll Robertson pupil is seen?

Answer 10

neurosyphilis, diabetes

Question 11

How is relative afferent pupil (Marcus Gunn) pupil caused? (Where is the lesion?)

Answer 11

lesion of the afferent limb of the pupillary light reflex

Question 12

How do you diagnose Marcus Gunn pupil?

Answer 12

swinging light reflex diagnosis made with swinging flashlight

Shine light in Marcus Gunn pupil > pupils do not constrict fully

Shine light in normal eye > pupils constrict fully

Shine light immediately again in affected eye > apparent dilation of both pupils because stimulus carried through that CN II is weaker; seen in MS

Question 13

Can enophthalmos be a feature of Horner’s syndrome? What is it?

Answer 13

yes; posterior displacement of the globe in an anteroposterior plane within the orbit.

Question 14

What is Adie pupil caused by?

Answer 14

ciliary ganglion lesion

Question 15

Symptoms of Adie pupil?

Answer 15

dilated pupil that reacts sluggishly to light, but better to accommodation; often seen in women and often associated with loss of knee jerks

Question 16

What eye symptom does transtentorial uncal herniation lead to and what is the pathology?

Answer 16

increased intracranial pressure> leads to uncal herniation > CN III compression> fixed and dilated pupil, “down and out” eye, ptosis

Question 17

What type of light do rods respond to?

Answer 17

• achromatic
• low - light sensitive
• night vision, motion

Question 18

What type of light do cones respond to?

Answer 18

• red, green, blue
• chromatic
• bright light sensitive
• object recognition

Question 19

Lesion of the left optic nerve?

Answer 19

anopia of left eye

Question 20

Lesion of lateral part of left optic nerve?

Answer 20

left nasal hemianopia

Question 21

A lesion of the optic chiasm?

Answer 21

bitemporal heteronymous hemianopia

Question 22

A lesion of the left optic tract?

Answer 22

right homonymous hemianopia

Question 23

Lesions damaging Meyer’s loop leading to the lingual gyrus on the left?

Answer 23

right homonymous superior quadrantanopia

Question 24

Lesions damaging the fibers going to the cuneus gyrus on the left side.

Answer 24

right homonymous inferior quadrantanopia

Question 25

If there was a lesion of the posterior cerebral artery of the left side what would the eye defect be?

Answer 25

right homonymous hemianopia with macular sparing

Question 26

What conditions can lead to lesions of the optic nerve?

Answer 26

optic neuritis, central retinal artery occlusion

Question 27

What conditions could lead to lateral occlusion of the optic nerve?

Answer 27

internal carotid artery aneurysm

Question 28

What can cause obstruction of the optic chiasm?

Answer 28

• pituitary adenoma (begins as superior quadrantanopia )
• craniopharyngioma (begins as inferior quandrantonopia

Question 29

Lesions past the optic chiasm produce ipsilateral or contralateral defects?

Answer 29

contralateral defects

Question 30

What are some lesions that can cause damage to the optic tract?

Answer 30

vascular

Question 31

How does MS affect the optic nerve?

Answer 31

unilateral optic nerve lesions are seen in MS, where there is an immune related inflammatory demyelination of the nerve. Lesion typically presents with a central scotoma due to involvement of deep fibers in the nerve from the macula