Mod 11 Visual System Flashcards
What is a visual field?
the portion of space that can be viewed from the retina when the eye is fixated straight ahead (what we see in the environment)
What is a retinal field?
the portion of retina that alters its firing rate in reasons to a stimulus (picks up light and color)
What is the relationship between visual and retinal field?
reverse and inverted relationship (temporal visual field is the nasal retinal field)
How are visual deficits named?
according to visual field
How is the retina divided?
- lateral: temporal
- medial: nasal
- superior and inferior half
What are rods and cones and where are they located?
- deepest retinal layer
- photoreceptors
What are the bipolar cells in the retina and where are they located?
- intermediate retinal layer
- info integrating neurons
What are the ganglion cells in the retina and where are they located?
- superficial layer
- info integrating neurons that exit the eyeball as the optic nerve (CN II)
What is the scotopic-rod system?
- system that works at low levels of light and is sensitive to light, insensitive to color
- limited resolution
What does the rod system help you do?
help see in the night vision
What is the photopic-cone system?
- system that works at high levels of light and is responsible for seeing color, sharp vision, and acuity
- color, clear
What color do rods see?
black, white, grey
What do rods and cones respond to?
respond to photons and signal retinal ganglion cells
How many rods and cones are in each eye?
80-110 million rods
4-5 million cones
Where are cones the densest in the eye?
densest in the macula
peripheral layers are where cones lie
What is the center of the macula?
fovea: area keenest vision
What is the memory trick remember cone’s role in the eye?
cones, color, clear
rods: light, peripheral
What is the role of ganglion cells in the eye?
center for retinal processing as it converges onto these cells
these cells form the optic nerve
Where do M Type ganglion cells project?
project to the magnocellular layer of the lateral geniculate body
What are M Type ganglion cells concerned with?
patterns and contrast
Where do P Type ganglion cells project?
parvocellular layer of lateral geniculate body
What are p type ganglion cells concerned with?
color transmission
What is the blind spot of the eye?
an elevated circular retinal region where ganglion cell axons leave the eye as the optic nerve
does not have rods and cones
What is the visual pathway?
receptors > bipolar cells(1st order) > ganglion cells (2nd order)/optic nerve > thalamus lateral geniculate body (3rd) > primary visual cortex
Which retinal field crosses in the optic chiasm?
nasal retinal fields
Which part of the nervous system is the optic nerve a part of?
CNS
What is the structure of the optic nerve?
- myelinated by oligodendrocytes
- invested by dural sheet of CNS
- surrounded by CSF
Where do optic nerve fibers originate?
originate in ipsilateral eye
What retinal fields are in a optic tract fiber?
temporal retinal field of ipsilateral eye and nasal retinal field of contralateral eye
Where do most axons of the optic tract synapse?
on third order neurons in the lateral geniculate body of the thalamus
Where does the LGB input come from?
10-20% from retina
rest comes from brainstem reticular info (arousal and consciousness) and visual cortex
Where do third order neurons go?
project from the LGB as optic radiation to the occipital lobe
Where do dorsal and ventral axons project in the brain?
dorsal: directly to occipital lobe
ventral: anteriorly and downward as Meyer’s loop
What is the inversion of visual fields in the eye?
upper visual fields project to lower retinal quadrants
nasal to temporal
Where does lower visual field input go in the visual pathway?
upper retinal quadrant goes dorsal to the primary visual cortex
Where does upper visual field input go in the visual pathway?
lower retinal field goes to Meyer’s loop then PVC
How do you remember what visual field goes to Meyer’s loop?
What I see higher goes meyer
What does the calcarine sulcus do?
splits retinal field input
Which broadmann’s area is the PVC?
BA 17
Where do some optic radiation axons terminate?
un visual association cortex BA 18 and 19
Where does the dorsal pathway of visual processing go and what does it process?
- PVC to parieto-occipital cortex
- WHERE in the visual field an event occurred
Where does the ventral pathway of visual processing go and what does it process?
- primary visual cortex to occipito-temporal cortex
- WHAT the object in the visual field is
Where do some optic tract axons terminate?
hypothalamus: role in circadian rhythm
Why do some optic tract axons bypass the LGB and project to the midbrain?
superior coliculus: visual grasp reflex
pretectal area: visual light reflex
How does aging affect the eye?
presbyopia develops
- age related loss of accommodation power (change focal length)
- lens hardens
- cannot focus on near objects
What is age related macular degeneration?
6th decade of life
- loss of central vision and acuity
- affects cone system
- leading cause of blindness in elderly
How do you assess the visual system?
- snellen chart
- ophthalmic inspection
- pupillary light reflex
- quadrant assessment
What is found in ophthalmic inspection?
optic dic swelling with elevated intracranial pressure due to excessive CSF
can cause blurred, double, or transient full vision loss
What is hemianopsia?
visual deficit of one-half of visual field
ex: temporal half
What is quadrantanopsia ?
visual deficit of one quadrant of the visual field
ex: upper temporal quadrant
What is bitemporal hemianopsia?
lesion to optic chiasm causing the loss of peripheral vision (severs nasal retinal fields)
What is contralateral homonymous hemianopsia?
lesion impacting optic tracts
- cannot see temporal retinal field of ipsilateral eye and nasal retinal field of contralateral eye
What is monocular scotoma?
individual blind spot
What is monocular visual loss?
whole eye blindness
What is contralateral inferior quadrantanopsia?
lower quadrant loss
What is contralateral superior quadrantanopsia?
upper quadrant loss
What is macular sparing?
vascular lesion to occipital lobe
- both MCA and PCA nourish cortical area for macula
- if one is occluded, the other still gives blood leaving you with central vision
What is amaurosis fugax?
transient ischemic attack of the retina
What is optic neuritis?
inflammatory demyelination disorder related to MS
- symptoms of: eye pain, decreased acuity, and impaired color vision, altered light reflex
- recovery is common
What is visual agnosia?
deficit associated with higher cortical processing when you can perceive but not understand what you see (ventral pathway)
What is prosopagnosia?
deficit associated with higher cortical processing that causes face blindness due to damage to the occipitotemporal cortex
What are the first signs of MS?
optic neuritis, scotoma, and visual field deficits due to the loss of oligodendrocytes
How do migraines connect with the visual pathway?
prodromal phase of migraine involves visual cortex
- 1/3 experience visual aura
- 10% experience scintillating scotoma where the blindspots are wavy, jagged, large, and bilateral in presentation
