Lecture 22 Clinical Vision - Harvard...
Transcript of Lecture 22 Clinical Vision - Harvard...
Lecture 4: Eye Movements & Eye Loss
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Vision and BrainScience B44
Lecture 22ClinicalVision
Mike May, Blind Ski RacerRegains Vision
LASIK Surgery
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1. Eye problems2. Low Vision3. Blindness4. Restored sight5. Sensitive period
Clinical Vision
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Focus – getting it right
Transparency - cataracts,corneal damage
Retina – reading it out
1. Eye problems
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Accommodation
Hyperopia
Myopia
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lasik surgery for myopia
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2. Low Vision
Many vision problems arecorrected by glasses,medicine or surgery
But eye disease, poor healthor injury can causepermanent vision loss.
Total loss -- blindness
Partial -- "low vision."
Lecture 4: Eye Movements & Eye Loss
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2. Low Vision
20/70
Macular degeneration
Glaucoma
Cataracts
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2. Blindness
20/200 or visual fieldless than 20°
10% fully sightlessVisual experiences,
memories, dreams?Depends on age of
blindnessEven in late blind, varies
enormously
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Recruitment of visual cortex for other uses
Touch uses visual cortex in the blind, more so inearly blind than late.
In sighted individuals, activity of the visual cortexgoes down in a tactile task.
10Sad and hopeful dogs by Tracy
Table by GaiaRaised line drawing
Drawing and painting by the blind
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Drawing and painting by the blind
51 yrs old, totally blind from birthReaching direction similar to visual directionVision and touch: common representation of space?
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“Jars” by Blind artist Lisa FittipaldiExamples from paper by Elaine Besancon
Drawing and painting by the blind
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William Moyneux, whose wife was blind, askedphilosopher John Locke:
“Suppose a man was born blind and taught bytouch to distinguish between a cube and asphere. If his vision was restored, could hedistinguish which was which before touchingthem?”
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3. Restored sight
In case of cataracts or corneal damage,treatment is sometimes possible
What is recovered?Depends on age of loss and age of recovery
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iris
Cataract and its treatment
Remove cataract and insert new lens
Corneal transplant
"During the first weeks I had no appreciation ofdepth or distance; street lights were luminousstains stuck to the window panes, and thecorridors of the hospitals were black holes.” HS,corneal transplant after 22 years of blindness
If sight is restored after age 15 and was lostbefore age 3, little is gained even after manyyears
corneal transplant restored sight at 52
thought quarter moon was like slice of cake
struck by how objects changed in appearance fromdifferent perspectives
S.B.
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S.B. inTrafalgar
Square
Very successful as a blind personBut now felt handicapped for the first time.Three years after the operation, he gave upand committed suicide.
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Patient Mike MayBlinded by a chemical accident at age 3.Scarring prevented cornea transplant until recently.
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Sky diver, three gold and three bronze Paralympic skiingmedals, fastest blind skier in the world.At 45, vision restored by epithelial stem cell + corneareplacement.
The moment when the bandages came off and he saw hiswife for the first time was incredibly touching. 'I knewthat bunched-up cheeks meant a smile,' he said.
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Later that day, when his children came back from school,he realized just what she had meant about theirstunningly blue eyes.
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restored resolution not so good,legally blind
perception of colors relativelynormal
identifies outlined shapesbut not shapes defined by illusory
contourscannot identify a static cube, or
see it as a 3D structureno depth from shadingdifficulty identifying faces
“sad woman”24
But motion helps a lotCould identify walker
Severe neural loss—slowly recovering only some functions.
Catch a ballSkiing: vision now helps!
Rotating cube
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India has the world’s largest population of blind peopleBlindness in nearly 50% can be treated or preventedBut most cannot afford treatment.
Blindness in India
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How many objectsWhich is in front?
100%100%
100%50%
How many objects? 100% 0%
How many objects? 100% 0%
How many objects? 100% 0%
How many objects? 100% 80%
How many objects? 100% 70%
Stimulus Task Controls SK
How many objects? 100% 0%
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Lost before 3, restored after 15, only getRough shapesLittle integration of separate patchesPoor depthMotion helps
Restored vision
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Stereo Sue had vision all her life but notdepth from binocular disparity
When binocular function was restored,her depth vision quickly reachedalmost normal levels
Why was her restored function differentfrom Mike May?
Restored function
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MyopiaAmblyopia
4. Sensitive period Inuit school kids were near sightedTheir illiterate parents were far sightedSame effect in Hong Kong vs rural ChineseExperiments in chickens show thatImage focus on retina drives eye ball growthRead in bright light
Does near work cause myopia?
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Selective deprivation: kittensraised in striped environments
Patching one eye: effect on number ofcells receiving input from patched eye
Monocular deprivation in children
One eye deprived because of bad focus ormisconvergence
Other eye dominates, takes over larger share ofcortex
Depth perception from binocular cells is lostMakes deprived eye “amblyopic”Treatment is to patch dominant eyeStrengthens weaker eye but cannot restore
binocular cells
Inputs to brain compete for real estateExperience makes a difference during the
sensitive period, but not after itDuration:
Deprivation affects human vision during thefirst 7 years
Visual deprivation lasting beyond 3 yearspermits little or no subsequent recovery ofvisual function
Sensitive period
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Eye problemsLow visionBlindnessRestored sightSensitive period
1 Minute QuizReadings for Wednesday EA 23Observation Paper presentations
in section this week
Summary
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Myopia: short sighted, focus in front of retinaHyperopia: far sighted, focus beyond retinaAmblyopia: eye, retina OK, vision bad, effect of
visual deprivationLow vision: vision loss, not blind 20/70 to 20/200Cataract: cloudy lens produces glare, blur, low
contrastGlaucoma: high pressure in eye destroys optic
nerve fibersMacular degeneration: cell or blood vessel damage
reduces central visionSensitive period: deprivation during this period
impedes normal development of vision
Glossary