Refraction
Glaucoma &
Glaucoma test
Degree of cell
packing
in retina
Intrinsic Muscles of the Eye:
The Iris
• Iris
– circular.....constricts
– radial.....…dilates
• Dilating pupil for eye
exam: how to do it?
Pharmacology of
pupillary dilation:
Atropine
Intrinsic Muscles of the Eye:
Ciliary Muscle
• Ciliary muscle relaxed = tension on
zonular fibers = tension on lens =
flattened lens = distant focus
• Ciliary muscle contracted = tension on
zonular fibers reduced = less tension on
lens = lens becomes more spherical
=near focus
• Eye strain
Using a Microscope or Binoculars
Accommodation animation
1) Demonstrate
Convergence
2) Measure NPA
With Convergence
NPA Left eye _______________mm
NPA Right eye ______________ mm
Sex of subject ___ Age in months___
with corrective lenses/contacts? yes/no
Presbyopia
Disorders of Focus
• Myopia = nearsighted
– eyeball too long, cornea/lens to
“strong”
– image focused in front of retina
– correct with concave lens
• Hyperopia = farsighted
– eyeball too short, cornea/lens to
“weak”
– image focused behind retina
– correct with convex lens
• Astigmatism
– irregular surface of lens or cornea
Cataract
•
Extraocular muscles
• Actions of extraocular muscles
• Motor innervation by CN III, IV, VI
Strabismus= misalignment of eyes
Storytime
Suprachiasmatic
Nucleus for diurnal
cycling
Visual reflexes:
Aka. Area 17 and V1
Accomodation, Saccades,
Tracking, Pupillary reflex
Evolution of
Binocular
Vision
Mapping the
boundary of each
visual field
Retinotopy
Goliath?
The Retina
• Photoreceptors
– Rods
– Cones
• Bipolar cells
• Ganglion Cells
– axons converge at optic disk
– axons constitute optic nerve
• Horizontal cells
• Amacrine cells
Importance of
abundant
membrane
Visual Acuity
• 120,000,000 rods and
6,000,000 cones per retina
• 1,200,000 retinal ganglion
cells & axons
• 105:1 convergence ratio
• Fovea: cones only, 1:1
highest visual acuity but
poor sensitivity
Counting fingers and
Reading the Writing on the Wall
Demonstration
of
Blind Spot
(diagram)
•Differences due to opsin: 4 types
Trichromatic Theory of Color Vision
Web-based
color
deficiency test
Stargazing
Finding your car in a dark parking lot
Choosing socks
“Bleaching” of photopigments
Visual Purple
The Dark Current
Phototransduction
• In the DARK, rod is depolarized due to influx
of Na+ (called dark current)
• In the LIGHT, rod is hyperpolarized
• cGMP keeps Na+/Ca++ channels open
• Light results in decrease of cGMP and thus
closure of ion channels, and
• Hyperpolarization of cell, and
• Reduced release of Neurotransmitter Glutamate
Properties of Cortical Neurons
• Simple
– respond to
stationary bar of
light in certain
orientation
• Complex
– respond to moving
bar of light in
certain orientation
• Hypercomplex
– respond to moving
bar of light of a
certain length in a
certain orientation
Parallel Processing in the Cortex
• Motion
sensitive
• Color and
shape sensitive
Story of woman at
street crossing
Why so much emphasis
on the Visual System?