beyond the second dimensionbeyond the second dimensiondme.ap.nic.in/stereopsis.pdf · dr....

Dr. VidyavatiDr. VidyavatiProfessor of ophthalmologyProfessor of ophthalmology

Sarojini Devi Eye Hospital, HyderabadSarojini Devi Eye Hospital, Hyderabad

Beyond The Second DimensionBeyond The Second Dimension

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LATERAL EYES

FRONTAL EYES



Why two eyes ?Why two eyes ?

l Just to have a spare

l Wider field of vision when using two eyes

compared to one.

l Stereoscopic vision by blending slightly

dissimilar views of an object , which is then

seen singly and with depth.



Binocular viewingBinocular viewing



Stereopsis Stereopsis l The relative ordering of visual

objects in the third dimension



l Stereopsis is obtained from fusible

but disparate retinal images falling

within Panum’s area. While

horizontal disparity produces

stereopsis , vertical disparity does

not result in any such perception .



Panum’s areaPanum’s area

l Region around the horopter in horizontal space in

which single vision is present.

l Small in center, larger in periphery.



StereopsisStereopsis

l It is not a form of simple fusion

l Develops by the age of 3 months & is

established by 6 months

l It occurs when retinal disparity is too big to

permit simple fusion but not big enough to

elicit diplopia. ( A bridge between fusion

and diplopia )



l It ranges from 20 to 2000 ft

(7000 times the IPD)

l Stereo acuity is the smallest amount

of retinal image disparity that produces

stereopsis ,and is measured in seconds

of arc.

StereopsisStereopsis



Testing forTesting forstereopsis stereopsis

l Essentially the two eyes must be

dissociated, and presented with a

separate field of view and targets

with fiducial marks.



Categories ofCategories ofAvailable TestsAvailable Tests

l Self contained

- Two pencil test - Lang I & II

- Synoptophore - Frisby

l Those that need polaroid or red green

glasses

- Titmus fly - Random dot Butterfly

- Random dot - TNO

- Randot E

l Mentor B – Vat

l Bioptogram



Two pencil test



Synoptophore Synoptophore

l Slides are presented to the two eyes

at slightly disparate angles

l Used for testing gross stereopsis

l Braddick slides test detailed stereopsis



Lang TestLang Test

l Test I measures from 600 to 1200 sec

of arc

l Test II measures from 200 to 1200 sec

of arc

l Unique feature – No glasses need to be

worn for viewing the test plate



Titmus fly testTitmus fly test

Basis : Principle of linear polarization

Measures 40 to 3000 sec of arc

l Wings of the fly - 3000 sec

lLozenges - 40 to 800 secs

l Animals - 200 to 400 secs –



Principle

Images formed of dots which are displaced

in relation to one another, the intervening

space being randomly filled by dots. Each

eye sees a separate set of dots , which

when fused result in a stereo image.

Random dot tests



Random Dot Butterfly Random Dot Butterfly

l Butterfly

– Top of upper wings 2000 sec

– Bottom of lower wings 1150 sec

– Tip of abdomen 700 sec

l Circles 40 to 800 sec

l Animals 100 to 400 sec



l For infants ( 6 months onwards)

Randot stereo

smile test



l Randot for preschool children

l 80-400 sec of arc

Randot test



Randot ‘E’ TestRandot ‘E’ Test

l Direction of tumbling ‘E’ is an added

feature

l Can be done at varying distances

l Measures

– At ½ meter 50 secs of arc

– At 5 meters 504 secs of arc



TNO Test TNO Test

Principle : Random dot and anaglyph

images. ( Viewed with Red & Green glasses )

l Used for quantitative assessment of

stereo acuity without changing distance

l Range 15 to 480 secs of arc



Anaglyphs Anaglyphs



MentorMentorBB--Vat system Vat system

l Measures distance stereo acuity

l Done with tumbling ‘E’ image

l Liquid crystal glasses and microprocessor

attachment

l Screen presents disparate images that

alternate rapidly ( 60 cycles / sec )



Bioptor Vision TestsBioptor Vision Tests

l Test 5a – for measuring distance stereo

acuity

l Range A to F measures 400 to 24 sec arc

l Useful in binocular imbalance (with eso or exo

bias)



BioptogramBioptogram



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beyond the second dimensionbeyond the second dimensiondme.ap.nic.in/stereopsis.pdf · dr....

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