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Stereopsis
Presented by ;
Shoaib khattak
Ojala nayab
Kainat akbar
M zafar
Shoukat ali
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To be discussed
 BSV and its stages
 Monocular depth clues
 Binocular disparity or stereopsis
 Stereo aquity
 How to test stereopsis
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Binocular single vision
 It is the coordinated use of both eyes to produce a single mental
impression
or
The simultaneous use of both eyes to produce a single mental
impression is called binocular single vision
It has three stages
 Simultaneous perception
 Fusion
 Stereopsis
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 Simultaneous perception
When signals transmitted from both eyes to visual cortex are
perceived at the same time .
 Fusion
It implies the ability of two eyes to form one image .
 Stereopsis
Three diamentional image perception during binocular vision is called
stereopsis .
Depth perception
Depth can be perceived by two ways
 Monocular depth clues
 Binocular disparities or stereopsis
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Monocular depth clues
 Monocular depth clues are also important for depth and distance
perception of objects .
 It includes
 Motion parallax
 Light and shade
 Linear perspectives
 Object overlap
 Relative size of objects
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 Motion parallix
 Stationery objects that are closer to the moving observer appears to
be moving faster .
 Linear perspectives
 The farther away the object is the smaller it appears to be .
 Object overlap
 Object slightly covered by another object appears to be farther away
 Light and shade
 Objects further off appears less saturated and less sharp than those of
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Binocular disparity or stereopsis
 Stereopsis is the visual perception of three diamentions during
binocular vision
 It results when horizontally disparate retinal elements are stimulated
simultaneously.
 Vertical disparaties produce No stereoscopic effect
 For example a solid object placed in the medium plan of the head
produces unequal images in the two eyes due to horizontal separation
of the two eyes .
 The sensory fusion of the two unequal images results in a three
diamensional percept .
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Types of stereopsis
 Coarse stereopsis
 it is that type of stereopsis which provide sense of being immersed in
ones soroundings
 Also called gross stereopsis
 It is important for orientation in space while moving
 Fine stereopsis
 This is very fine amount of depth perception between two objects
 It is important for fine motor tasks such is threading a needle
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Stereoaquity
 Stereo aquity is the angular measurement of minimal resolvable
binocular disparity which is necessary for perception of three
diamentional images .
 It is measured in seconds of arc
 The normal level of stereo aquity is being 40 sec of arc
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Test for stereopsis
 Lang two pencil test
 Frisby stereo aquity test
 Random dot stereogram
 Lang stereo test
 TNO test
 Lang II test
 Titmus fly test
 Randot stereotest
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Lang two pencil test
 This test is performed for gross stereopsis
 The patient attempts to place a pencil tip on top of the one held by
the examiner .
 Patients who have normal stereopsis will find it easier to perform the
test binocularly than monocular .
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 It consists of three plastic plates of different thickness 6mm,3mm,and
1mm.
 Each plate consists of four squres formed by random shapes formed
on one side of it .
 Corresponding to one of the squares a disparity is produced .
 This disparity creates a 3D appearance of a circle .
 The plates are held at 40 cm normally .
Frisby stereo aquity test
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Stereo aquity chart
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Random dot stereogram test
 It comprises images formed of dots which are displaced in relation to
each others .
 Both eyes will see different dots
 The space between images is filled randomly by dots .
 Following are two types of random dot stereogram test
 Lang stereo test
 TNO test
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Lang stereo aquity test
 Developed by swiss ophthalmologist joseph lang
 Available in two versions as lang I and lang II which only differs in the
type of stereoscopic objects to be recognized .
 The lang II test additionally contain a picture that can be recognized
with one eye as a star .
Procedure
 Show the test plate exactly at right angle at a distance of 40 cm to
the patient .
 Ask the patient if he/she could something on the plate and watch the
searching movement of the eye .
 When a 3D object is detected ask the patient to look for additional
objects and to describe them
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 Disparities in lang I
 Car ; 550 sec of arc
 Star ; 600 sec of arc
 Cat ; 1200 sec of arc
 Lang II
 Moon ; 200”
 Truck ; 400”
 Elephant ; 600”
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TNO test
 This test was primarily designed for screening of pre school children
for binocular vision defects .
Procedure
 It consists of seven plates to be viewed with red green spectacles that
carry figure which are only seen when both eyes coordinate to give
stereoscopic vision .
 Test should be carried out at a distance of 40cm .
 The plates should not be rotated during test procedure.
 Spectacles should not be removed
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 The 1st three plates enable the examiner to quickly asses whether the
stereopsis is present or absent .
 The next four plates are used for exact determination of stereoscopic
vision.
 Plate V measure stereoscopic aquity of 480-240 sec of arc .
 Plate VI measure upto 120-60 sec of arc
 Plate VII measures stereoaquity of 30-15 sec of arc .
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Plates composition
 Plate I is composed of two butterflies one of them is hidden and can
only be seen when both eyes are used .
 Plate II contains 4 discs that differs in size .
 Two of them are larger and other two are smaller.
 The smaller plates can only be seen when there is adequate
stereopsis .
 Plate III have four hidden structures like square ,triangle or discs
arranged around a central cross.
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 Plate IV:
 this is a suppression test .
 It consists of a small disc and two large dics .
 If a patient see only two dics one small and one large . it indicates
suprresion.
 The large disc is seen through dominant eye .
 Plate V-VII; contain discs that are presented to patient at six different
disparity levels ranging from 15 to 480 sec of arc
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Titmus fly test
 It is based on principle of linear polarization .
 Polarized filters are worn and vertical image of a light source is seen
through one filter and horizontal image is seen through other eye .
 The target are presented as vectograph .
 The disparity produced by either eye results in stereopsis .
 One plate contains the image of a fly .
 The 2nd plate consists of nine boxes each containing 4 circles and
three rows of animal.
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Procedure
 The patient wear polarized filters over his/her correction.
 Patient is 1st shown the plate that contain fly .
 The patient is instructed to catch the fly by its wings .
 If the fingers reach above the plate the patient has stereopsis .
 If the fingers touches the plate then there is No stereopsis
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Randot stereo aquity test
 This test is similar to titmus fly test .
 One plate is consists of two groups of four squares three of those
squares contain circle ,square and star .
 The other plate consists of animals and circle .
 The perception of random shapes give stereoaquity of 500-250 sec of
arc.
 The perception of animal shapes give stereoaquity of 400-20 sec of
arc.
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Keep smiling and enjoy the depth of
nature
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