Beyond The Second DimensionBeyond The Second Dimensiondme.ap.nic.in/STEREOPSIS.pdf · Dr. VidyavatiDr. Vidyavati Professor of ophthalmology Sarojini Devi Eye Hospital, Hyderabad Beyond

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. VidyavatiDr. Vidyavati Professor of ophthalmology Sarojini Devi Eye Hospital, Hyderabad Beyond

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