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."


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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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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



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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%





Stimulus Task Controls SK


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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

lecture 22 clinical vision - harvard...

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