vision & perception
DESCRIPTION
Dr. Raj Patel OD - Vancouver Vision Clinic. Vision & Perception. What we will cover today…. Eye Anatomy Accommodation Rods & Cones Convergence Edge Enhancement (Herman Grid Illusion) Contralateral Processing Cases. LE 49-18. Photoreceptors: Rods & Cones 160K/mm in humans, - PowerPoint PPT PresentationTRANSCRIPT
Vision & PerceptionDr. Raj Patel OD - Vancouver Vision Clinic
What we will cover today…Eye Anatomy AccommodationRods & ConesConvergenceEdge Enhancement (Herman Grid
Illusion)Contralateral ProcessingCases
LE 49-18
Cornea
Ciliary body
Suspensoryligament
Iris
Pupil
Aqueoushumor
Lens
Vitreous humor
Central artery andvein of the retina
Optic disk(blind spot)
Fovea (centerof visual field)
Opticnerve
RetinaChoroidSclera Photoreceptors:
Rods & Cones160K/mm in humans, 1 Billion/mm in hawk
Retinal image (? Eye)
Retinal Detachment
Cataract
Cataract surgery
LASIK surgery
Accomodation
The lens inside the eye changes shape to focus at different distances
LE 49-19
Retina
Choroid
Suspensoryligaments
Front view of lensand ciliary muscle
Ciliarymuscle
Lens (rounder)
Lens (flatter)
Near vision (accommodation)
Distance vision
What happens after 40!
Presbyopia
How do we see ?
Lets go back to the retina …
LE 49-22Light Responses
Rhodopsin active
Na+ channels closed
Rod hyperpolarized
Bipolar cell eitherhyperpolarized ordepolarized, depending on glutamate receptors
No glutamatereleased
Dark Responses
Rhodopsin inactive
Na+ channels open
Rod depolarized
Bipolar cell eitherdepolarized orhyperpolarized, depending on glutamate receptors
Glutamatereleased
Rods:1. More sensitive to light – function better in dim light2. Become bleached in bright light3. Absorb all wavelengths of visible light, so they give monochrome vision4. Groups (up to 200) pass impulses to same sensory neuron of optic nerve, therefore less visual acuity5. More widely dispersed, giving a wider field of vision
Cones:1. Less sensitive to light2. Don’t bleach in bright light, function well in bright light3. 3 types of cone cells: sensitive to red, green & blue light4. Have their own individual neuron through which messages can be sent to brain, therefore better visual acuity5. Very concentrated near the fovea, giving one acute area of field of vision
General Organization
Retina is only part of CNS visible 3 layers of neurons
More Detail of Cell TypesReceptive field, convergence, resolution
So how do we process all this?
Edge Enhancement
background
Provides greater contrast Many rods -> single ganglia = lower
acuity Cones have lower ratio with ganglia
= higher acuity Receptive fields. If smaller then
higher acuity Large fields in peripheral retina /
smallest in fovea
The concept
Lateral Inhibition 2 other cells (horizontal and
amacrine) Below is 1 to 1 mapping (fovea)
Drum roll …
Herman Grid IllusionDue to edge enhancement white areas of grid look whiter if they are next to black area
Optical illusion: grey areas appear at the intersections of the white lines which are not real. If all of grid is covered up apart from one white line, the grey areas disappear.
Still Awake
Contralateral Processing
Collect - integrate - perceive
LE 49-24Leftvisualfield
Rightvisualfield
Lefteye
Righteye
Primaryvisual cortex
Lateralgeniculatenucleus
Optic nerve
Optic chiasm
3. Contralateral processing of Visual Stimuli*Both retinas receive stimuli from left & right fields of vision*Left & right optic nerves cross in optic chiasma*Right field of vision is processed in left side of brain (vice versa)*Neurons from optic nerve synapse with neurons in visual cortex of Cerebrum (occipital lobe)*Allows brain to Have perception of depth, distance & sizes
An interesting case
Where is the problem located?
Thank You