Glaucoma & Glaucoma test Refraction Degree of cell packing in retina.
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Transcript of Glaucoma & Glaucoma test Refraction Degree of cell packing in retina.
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Glaucoma &
Glaucoma test
Refraction
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Degree of cell packingin retina
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Intrinsic Muscles of the Eye:The Iris
• Iris– circular.....constricts– radial.....…dilates
• Dilating pupil for eye exam: how to do it?
Pharmacology ofpupillary dilation:
Atropine
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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
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With Convergence
1) DemonstrateConvergence
2) Measure NPA
Accommodation animation
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NPA Left eye _______________mmNPA Right eye ______________ mm
Sex of subject ___ Age in months___
with corrective lenses/contacts? yes/no
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Presbyopia
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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
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Cataract
•
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Extraocular muscles
• Actions of extraocular muscles
• Motor innervation by CN III, IV, VI
Strabismus= misalignment of eyes
Storytime
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Suprachiasmatic Nucleus for diurnal cycling
Visual reflexes:
Accomodation, Saccades,
Tracking, Pupillary reflexAka. Area 17 and V1
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Evolution ofBinocular
VisionMapping the boundary of each visual field
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Retinotopy
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Goliath?
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The Retina
• Photoreceptors– Rods– Cones
• Bipolar cells• Ganglion Cells
– axons converge at optic disk– axons constitute optic nerve
• Horizontal cells• Amacrine cells
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Importance of abundantmembrane
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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 andReading the Writing on the Wall
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Demonstrationof
Blind Spot(diagram)
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•Differences due to opsin: 4 types
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Web-based color deficiency test
Trichromatic Theory of Color Vision
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StargazingFinding your car in a dark parking lot
Choosing socks
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Visual Purple
“Bleaching” of photopigments
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The Dark Current
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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
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Properties of Retinal Ganglion Cells
• Use MacRetina software to simulate experiments of Hubel & Wiesel (1960s)
• Determine location and shape of “receptive field” of an RGC.
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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
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Parallel Processing in the Cortex
• Motion sensitive
• Color and shape sensitive
Story of woman atstreet crossing
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Why so much emphasis on the Visual System?