Chapter 11 (10.14) Flashcards
From chapter 11-12 powerpoint
Define homonymous in terms of visual field defects
The visual field loss affects the same side of both eyes
A greater portion of our brains are devoted to _________ than to any other sensory modality.
sight
Light enters the eye’s lens and forms an image on the retina that is of what orientation?
Inverted and reversed
Why are images inverted on the retina?
Information from the upper visual field is projected onto the lower retina, and vice versa
Information from the lower visual field is projected on the ___________ retina
upper
Why are images reversed on the retina?
The right visual field projects onto the left retina (and vice versa) of each eye
The left visual field projects onto the ____________ retina of each eye
right
The central fixation point for each eye falls onto the _____
fovea
What is the fovea?
The central fixation point for each eye
Define hemianopia
Loss of half of the visual field of an eye
What is the optic disc?
The area where axons leave the retina and gather to form the optic nerve
Photoreceptors (rods and cones) respond to what?
Light
1) Photoreceptors (rods and cones) respond to light and send excitatory or inhibitory synapses where?
2) What do those things then synapse onto? What does that thing do?
3) Where is all of this happening?
1) Onto bipolar cells, which synapse onto
2) Ganglion cells; send their axons to the optic nerve
3) In the retina
What area doesn’t have photoreceptors over it?
The optic disc
Where is our blind spot?
Slightly inferior and lateral to the central fixation of each eye
What part of the eye creates the blind spot?
Optic disc
Why are we usually not aware of our blind spot?
Our visual analysis pathways fill this in
What happens at the optic chiasm?
There is a partial crossing of fibers
Explain the crossing over of fibers at the optic chiasm
1) Fibers from the left hemiretina of both eyes end up in the left optic tract (and vice versa)
2) Lateral (temporal) fibers don’t cross over, but medial fibers do
Fibers in the right hemiretina end up in the ____ optic tract
right
What fibers don’t cross over in the optic chiasm?
Lateral (temporal) fibers
Lesions anterior to the [optic] chiasm produce what kind of visual field defects?
monocular
Lesions posterior to the optic chiasm produce what kind of visual field defects?
homonymous (same place in both eyes)
Medial fibers represent what field of vision after crossing over?
The lateral fields of vision of both eyes
Lesions of the optic chiasm produce what kind of visual field defects?
bilateral lateral
Describe the location of the optic chiasm:
1) What surface of the brain is it on?
2) Where is it in relation to the frontal lobes?
3) Where is it in relation to the pituitary gland?
1) On the ventral surface of the brain
2) Inferior to the frontal lobes
3) Anterior to the pituitary gland
A tumor on the what part of the brain can press on the optic chiasm?
Pituitary
A tumor on the pituitary can press on the optic chiasm and cause what kind of field defects?
Bilateral temporal (aka bitemporal hemianopia)
The optic tract wraps around the midbrain, then to where?
The lateral geniculate nuclei (LGN) of the thalamus
The LGN is in what part of the brain?
Thalamus
What can can result in bitemporal hemianopia? Why?
Pituitary adenomas; from compression of the optic chiasm
Why do pituitary adenomas cause the visual effect they do?
They press on the optic chiasm, compressing the medial fibers, which convey the outer half of vision for both eyes
What can bitemporal hemianopia result from?
Pituitary adenomas
Axons of the retinal ganglion cells in the optic tract synapse onto neurons on the LGN of the thalamus, then where do they go?
Superior colliculus
What happens after vision reaches the superior colliculus?
Optic radiations project to the primary visual cortex
A small amount of the fibers rebel and bypass the LGN to form what?
The extra geniculate visual pathways to the superior colliculus (and pretectal area)
What is the superior colliculus important in?
Directing visual attention and eye movements towards visual stimuli
1) The superior colliculus and pretectal areas project where for visual attention?
2) How?
1) To the brainstem and association cortex
2) Via relays in other thalamic nuclei
What are the functions of the other thalamic nuclei that project the superior colliculus to the brainstem?
Visual attention/orientation/discrimination/perception (i.e. help us direct our attention to something seen or heard)
1) How many layers does the LGN have?
2) What do those neurons do?
1) 6 different layers.
2) Participate in motion, spatial awareness, and color vision.
What do the neurons of the LGN do?
Participate in motion, spatial awareness, and color vision.
True or false: Information from the left and right eyes remain segregated after passing through the LGN
True
Where do the axons leaving the LGN go?
To the superior colliculus, then back toward the primary visual cortex in the occipital lobe.
What fans out over a wide area to form the optic radiations?
The superior colliculi
True or false: Axons from both sides of the LGN intermingle
True
Lesions of the optic radiations usually cause what kind of visual defects?
Bilateral homonymous
What pathway is likely defective if color vision isn’t working?
The LGN
What are the two sets of questions you should ask a patient to assess their visual disturbances?
1) What is the nature of the disturbance? Time frame, colored lights, blind spots?
2) Description of the visual fields. One or both eyes? What part of visual field? Is it the same in both eyes?
Define scotoma
A blind spot in the visual field
On imaging, how do you know if you’re looking at the optic disc or a blind spot?
The optic disc will always be lateral and inferior to central vision
Visual hallucinations come from what part of the brain?
The inferior temporo-occipital association cortex.
Name 8 common causes of visual hallucinations
1) Alcohol and drug withdrawal
2) Complex migraines
3) Psychiatric disorders
4) Toxic or metabolic disturbances
5) Hallucinogenics
6) Anticholinergics
7) Cyclosporine
8) Narcolepsy
If a pt is complaining of a blind spot on their upper right part of their right eye’s vision, where is their lesion?
In the lower left part of the retina (of the right eye)
If you have a lesion anterior to the chiasm on the right tract, what happens to vision?
Right eye vision is gone
If you have a pituitary adenoma pressing on the medial fibers on the optic chiasm, where do you lose vision?
Lateral fields of both eyes
Trace the path of blood flow to the retina (3 steps)
1) Internal carotids, which branches into
2) Ophthalmic artery, which branches into
3) Retinal artery
What are the 3 main causes of blood flow impairment to the retina?
1) Emboli (from carotid artery plaques)
2) Stenosis (DM/ HTN)
3) Vasculitis
Trace the path of blood flow to the retina (3 steps)
1) Internal carotids, which branches into
2) Ophthalmic artery, which branches into
3) Retinal artery
Central __________________ occlusion can cause infarction of the entire retina
retinal artery
Define Amaurosis Fugax
Transient occlusion of the retinal artery
1) What causes Amaurosis Fugax?
2) What is a common cause of that?
1) Emboli [occluding the retinal artery]
2) Ipsilateral carotid artery stenosis
Describe the symptoms of amaurosis fugax
1) “Browning out”; can also commonly be described as a “window shade going up or down” on one eye
2) Loss of vision in one eye for roughly 10 min.
If a patient describes having the visual of a window shade going up or down in one eye, what might they be having?
Amaurosis Fugax
What can Amaurosis Fugax be a signal of?
Impending retinal or cerebral infarct.
What can ipsilateral carotid artery stenosis cause?
An artery-to-artery emboli
(which can then travel and cause Amaurosis Fugax)
Define optic neuritis
An inflammatory demyelinating disorder of the optic nerve both pathophysiologically and epidemiologically related to Multiple Sclerosis.
Describe the demographic optic neuritis is often seen in
Mean age is 30s, 2:1 female to male ratio
What is are the symptoms of optic neuritis?
1) Causes eye pain especially with movement
2) Monocular vison problems; often a central scotoma, deceased acuity, and impaired color vision
_____ or more of patients with a clinically isolated episode of optic neuritis will eventually develop MS
50%
What is optic disc pallor a sign of?
Prior episodes of optic neuritis
If a patient complains of pain in one eye that’s worse with movement, what may they have?
Optic neuritis
