Visual System 2 and 3 Flashcards
Ganglion cell axons travel in the ______ to the ______
Optic nerve
Optic chiasm
At the level of the optic chiasm, axons coming from the lateral retina
DO NOT DECUSSATE and enter the IPSILATERAL optic tract
At the level of the optic chiasm, axons coming from the medial retina
DECUSSATE and enter the CONTRALATERAL optic tract
Fibers in each optic tract terminate in the
Lateral geniculate nucleus (the thalamic relay nucleus for vision) FIRST ORDER NEURONS
Geniculate fibers travel through the internal caps and corona radiate to
the primary visual cortex in the banks of the calcarine sulcus
A minority of fibers in the optic tract bypass the LGN to enter the
Brachium of the superior colliculus
Fibers that enter the brachium of the superior colliculus form the extrageniculate visual which mainly project to the
Pretectal area and superior colliculus
The pretectal area is important in the
Pupillary light reflex
The superior colliculus and pretectal area are also involved in
Directing eyes towards visual stimuli
Fibers arising from the lateral geniculate nucleus (2nd order) curve around the lateral wall of the lateral ventricle as
Optic radiation
Optic radiation terminates
In the cortex adjacent to the calcarine sulcus
Optic radiation covers
Much of the posterior and inferior horns od the lateral ventricle
Fibers representing superior retivisual quadrants loop our into the ______ before turning posteriorly
Temporal
Upper retina projects to cortex
Above calcarine sulcus
Lower retina projects to cortex
Below calcarine sulcus
Macula projects to cortex
Middle area, posteriorly
Lesions where often cause visual loss in one quadrant of the visual field with MACULAR SPARING
Optic radiation
GIVEAWAY FOR OCCIPITAL LOBE
Peripheral fields project to cortex
Anteriorly
What represents a large area of the primary visual cortex?
Macula
Blood supply of optic radiations
Branches of middle cerebral arteries that penetrate deep into white matter
Blood supply of visual cortex
Posterior cerebral cortex
Visual field defects are named according to
Visual field loss and NOT according to the area of the retina or optic pathway that is nonfunctional
Blindness
Loss of the whole visual field
Hemianopia
Loss of half a visual field
Quadrantanopia
Loss of one quarter of a visual field
Homonymous
Same field lost in both eyes
Heteronimous
Opposite field lost in both eyes
Lesion before the chiasm
One eye is affected
Lesion after the chiasm
Both eyes are affected
Blind, right eye
Optic nerve, embolism from internal carotids
Bitemporal hemianopia
Optic tract, pituitary tumor (compresses optic chiasm in the middle)
Left hemianopia, right eye
Ischemia, tumor, aneurysm (compresses optic chiasm from the side)
Left homonymous hemianopia
Ischemia, tumor, aneurysm (compresses optic chiasm from the side)
Left superior quadrantanopia
Ischemia or infarct in the temporal lobe (MCA) (affects anterior area of Meyer’s loop)
Left homonymous hemianopia
Ischemia or infarct in the temporal and occipital lobe (MCA or PCA) (affects both loops)
Left inferior quadrantanopia
Ischemia or infarct in the parietal or occipital lobe (MCA or PCA, affects superior loops)
Left superior quadrantanopia
Ischemia or infarct in the temporal or occipital lobe
MCA or PCA, affects inferior loops
Inferior loop AKA
Meyer’s loop
Quadrantanopia with macular sparing
Ischemia or infarct affecting superior or inferior optic radiation, macula is spared because it is presented in BOTH parts of the optic radiation
Superior radiation affected = ______ quadrantanopia
Lower
Inferior radiation affected = ______ quadrantanopia
Upper
Hemianopia with macular sparing is caused by
Ischemia or infarct affecting occipital lobe supplied by PCA
Why is the macula spared?
The region of the occipital lobe where the macula is presented is saved by collaterals coming from the MCA territory
Receptor potentials in photoreceptors are the beginning of a neural process in which patterns of light are dissected into their components, which are:
Motion, boundaries between light and dark areas, and areas of different color
The brain makes its “best guess” in interpreting patterns of light and the results are sometimes
Inaccurate or go considerably beyond the information received by the eye
Most input to primary visual cortex arrives at cortical layer
4
Divisions of layer 4
Sublaminae 4A, 4B, 4Ca and 4Beta
Layer 4B contains numerous
Myelinated axon collaterals resulting in the pale-appearing stria of Gennatti
Primary visual cortex is also sometimes called
Striate cortex
From primary visual cortex (area 17), neurons project to
the visual association cortex (areas 18 and 19) and other regions of the parieto-occipital and occipitotemporal cortex
The dorsal pathways project to
Parieto-occipital association cortex
The ventral pathways project to
Occipitotemporal association cortex
The dorsal pathways answer the question _____? by ______
Where
By analyzing motion and spatial relationships between objects as well as between the body and visual stimuli
The ventral pathways answer the question _____? by ______
What
By analyzing form, with specific regions identifying colors, faces, letters, and other visual stimuli
The parallel channel layers conveying information about movement and gross spatial features project to
Layer 4Ca
The parallel channel layers carrying fine spatial information terminate in
Layers 4Cb
The parallel channel information about color is relayed to
Cortical layers 2 and 3
Prosopagnosia
Patients are unable to recognize people by looking at their faces
Lesion that causes prosopagnosia
Bilateral inferior occipitotemporal cortex (AKA fusiform gyrus)
Some evidence suggests that the _____ hemisphere is more important in facial recognition
Right
Patients with prosopagnosia cannot recognize people by their faces, but can recognize them based on
their clothes, voices, or other cues
Agnosia
Normal perception but no meaning
Hemineglect syndrome
Patient perceives only the right half of an object or eats food only on the right half og the plate
Normally, the left hemisphere is
Aware of the right part of the world around us
Normally the right hemisphere is
Aware of both sides, with only slight dominance to the left
In hemineglect syndrome, the visual fields are affected how?
They are intact
In hemineglect syndrome, where is the damage?
Right hemisphere, right parietal lobe
Easy way to test hemineglect syndrome?
Draw a line and ask patient to mark the center
Amblyopia
AKA lazy eye, is decreased vision in an eye that is otherwise normal
Whenever the brain does not receive visual signals from an eye for a long period of time, there is a risk of
Amblyopia
Why does amblyopia occur?
The brain turns off the visual processing of one eye to prevent double-vision, the cause is in the brain
Detecting what early in childhood increases the chance of successful amblyopia treatment?
Strabismus
Especially if before age 5
Strabismic amblyopia
Most common, to avoid double vision caused by poorly aligned eyes, the brain ignores visual input from the misaligned eye, leading to amblyopia in that eye
Refractive amblyopia
Caused by unequal refractive errors in the two eyes despite perfect eye alignment (ie. severe hyperopia or myopia in one eye, or astigmatism in one and not in the other) so the brain relies on the eye that has less uncorrected refractive error and “tunes out” the blurred vision from the other eye, causing amblyopia from disuse
Deprivation amblyopia
Caused by something that obstructs light from entering and being focused in a baby’s eye (like a congenital cataract) Prompt treatment of congenital cataracts is necessary to allow normal visual development to occur
Giveaway symptom: sudden vision loss in one eye
Embolism
Giveaway symptom: veil falling, black curtain
Retinal detachment
Giveaway symptom: Floaters (dust particles, lint, moving black spots)
deposits of various size, shape, consistency, refractive index, within the vitreous humor, which is normally transparent
Develop with age due to degenerative changes of the vitreous
Perception of floaters
myodesopsia
Pain and redness
Acute angle closure glaucoma (increased IOP)
Most often leads to defects in the draining of the intraocular fluid
Emergency - can lead to blindness
Redness with watery discharge, both eyes affected
Viral conjunctivitis
Redness with purulent discharge, one or both eyes affected
Bacterial conjunctivitis
