Eyeball functions Name the structures and functions of retina Differentiate between cones and rods Draw central visual pathway Predict visual field defects ID: 913835
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Slide1
Visual System
Slide2Objectives
Eyeball
functions
Name the structures
and
functions
of
retina
Differentiate between cones
and
rods
Draw central
visual
pathway
Predict visual
field
defects
by
lesion
sites
Slide3Visual Perception
Refraction
of
lights
by
the
lens
and
cornea
Convert
the
electromagnetic
energy
in
light
by
the
retinal
photoreceptor
cells
into
nerve
impulses
Nerve
impulses
from
retinal
photoreceptor
to
visual
cortex
(occipital
lobe)
Perception
of
visual image in the primary visual cortex (V1). V1 projects to the adjacent visual association area for advanced processing.
Slide4Through the Lens (& Cornea)
Refraction of lights
Focused image on the retina
reversed and inverted
Ciliary
muscle regulates the lens curvature
Slide5Visual field vs. Retinal field
Binocular visual field
Slide6Retina: Photoreceptors
Cones
-less (30 million)
-central retina, fovea
-operate
under
bright light
-high visual acuity
-process all color shades
*3 types: blue/green/red
Rods
-more (100 million)
-retina, except fovea
-operate
under
dim light
-low visual acuity
-process
grayscale
color
Slide7Optic Disc – Optic Nerve
Ganglion cell axons converge at the optic disc
At optic disc, axons turn posteriorly and exit the retina to form optic nerve
Not in the middle
More towards nasal
No photoreceptor
Blind spot!
Slide8Exercise: Find your blind spot
Pick an eye
Close the other eye
Stare at the cross
Move your note around
Check if the black dot disappears in a specific location!
Slide9Exercise: 2 things to take away!
No photoreceptor, no visual information
The optic nerve is not in the middle of the retina, so the blind spot is in:
Right eye: right visual field
Left eye: left visual field
Test your right eye
Test your left eye
Slide10Video: visual pathway
https://www.youtube.com/watch?v=ETIp8kZPoBw
From visual field to visual cortex
Slide11Quick review
Slide12Visual Cortex
Slide13Visual Field Defect
Anopsia
A lesion at any point in the visual pathway
Causes: tumors, strokes,
etc
Loss of a specific point in the visual field
We will discuss 6 types
Slide14Video: visual lesions
https://www.youtube.com/watch?v=463SLpz7bxs
to
7
:20
Slide15Slide16Visual Perceptual Deficit
Visual
agnosia
Lesion in visual association cortex
Dorsal: Visual integrated motion, temporal, and spatial information
Ventral: Visual memory, object recognition, written information
Slide17Visual Perceptual Deficit
Left Neglect
Apperceptive
agnosia
Associative
agnosia
Prosopagnosia
Alexia
Agraphia
Optic aphasia
Slide18Left Neglect
Neglect
Fail to respond to the information on the
contralateral side
to the brain lesion
Can happen in either R/L hemisphere, but more common in RH damage
31% - 66% people with RHD show neglect
Slide19Left Neglect
An example:
https://www.youtube.com/watch?v=d4FhZs-m7hA
1:40, 3:20
Slide20Theories about Neglect
NOT due to:
Primary sensory deficit (e.g., visual pathway cut)
Motor deficit
Perceptual disorder
Deficit in space representation
Attention deficit
Most accepted theory
Severe neglect: ignore all the sensory inputs from the affected side
Slide21Prosopagnosia
Impaired ability to recognize faces
Famous people
Family members
In severe cases, people may not distinguish objects from faces
An example:
https://www.youtube.com/watch?v=vwCrxomPbtY
Slide22Visual Deficit Assessment
Some examples!
Slide23Line Bisection
Present a horizontal line and ask a person to label the middle of the line
Slide24Picture description
Present action scenes with details on both L & R side, and ask a person to describe it
Slide25Drawing