Chapter 8: Visual Pathways Flashcards
Can vitamin A be synthesized by humans?
no
Describe the route traveled of the pupillary light reflex pathway of the afferent limb CN II?
- 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))
Describe the efferent limb of the pupillary light reflex pathway.
Edinger Westphal nucleus (preganglionic parasympathetic) > ciliary ganglion (postganglionic parasympathetic) > pupillary sphincter muscle > miosis
M3 activation of the ciliary muscle causes what actions?
contraction > accommodation for near vision
M3 blockade causing blockage of ciliary muscle activation leads to what actions?
relaxation > focus for far vision
What 3 events occur when an individual focuses on a nearby object
- accommodation
- convergence
- pupillary constriction (miosis)
Describe how accomodation takes place?
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
Describe how convergence takes place?
both medial rectus muscle contract adducting both eyes.
A term used in general to describe Argyll Robertson pupil?
pupillary light-near dissociation
What are conditions in which Argyll Robertson pupil is seen?
neurosyphilis, diabetes
How is relative afferent pupil (Marcus Gunn) pupil caused? (Where is the lesion?)
lesion of the afferent limb of the pupillary light reflex
How do you diagnose Marcus Gunn pupil?
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
Can enophthalmos be a feature of Horner’s syndrome? What is it?
yes; posterior displacement of the globe… eyeball sinks into eye socket
What is Adie pupil caused by?
ciliary ganglion lesion
Symptoms of Adie pupil?
dilated pupil that reacts sluggishly to light, but better to accommodation; often seen in women and often associated with loss of knee jerks
What eye symptom does transtentorial uncal herniation lead to and what is the pathology?
increased intracranial pressure> leads to uncal herniation > CN III compression> fixed and dilated pupil, “down and out” eye, ptosis
What type of light do rods respond to?
- achromatic
- low - light sensitive
- night vision, motion
What type of light do cones respond to?
- red, green, blue
- chromatic
- bright light sensitive
- object recognition
Lesion of the left optic nerve?
anopia of left eye
Lesion of lateral part of left optic nerve?
left nasal hemianopia
A lesion of the optic chiasm?
bitemporal heteronymous hemianopia
A lesion of the left optic tract?
right homonymous hemianopia
Lesions damaging Meyer’s loop leading to the lingual gyrus on the left?
right homonymous superior quadrantanopia
Lesions damaging the fibers going to the cuneus gyrus on the left side.
right homonymous inferior quadrantanopia
If there was a lesion of the posterior cerebral artery of the left side what would the eye defect be?
right homonymous hemianopia with macular sparing
What conditions can lead to lesions of the optic nerve?
optic neuritis, central retinal artery occlusion
What conditions could lead to lateral occlusion of the optic nerve?
internal carotid artery aneurysm
What can cause obstruction of the optic chiasm?
- pituitary adenoma (begins as superior quadrantanopia )
- craniopharyngioma (begins as inferior quandrantonopia
Lesions past the optic chiasm produce ipsilateral or contralateral defects?
contralateral defects
What are some lesions that can cause damage to the optic tract?
vascular
How does MS affect the optic nerve?
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
