stereopsis .pptx

Binocular single vision and stereopsis

1. Stereopsis Presented by ; Shoaib khattak Ojala nayab Kainat akbar M zafar Shoukat ali 1

2. To be discussed BSV and its stages Monocular depth clues Binocular disparity or stereopsis Stereo aquity How to test stereopsis 2

3. 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 3

4. 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 4

5. 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 5

6. 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 near objects 6

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8. 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 . 8

9. 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 9

10. 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 10

11. 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 11

12. 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 . 12

13. 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 13

14. Stereo aquity chart 14

15. 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 15

16. 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 16

17. 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” 17

18. 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 18

19. The 1 st 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 . 19

20. 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. 20

21. 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 21

22. 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 2 nd plate consists of nine boxes each containing 4 circles and three rows of animal. 22

23. Procedure The patient wear polarized filters over his/her correction. Patient is 1 st 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 23

24. 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. 24

25. Keep smiling and enjoy the depth of nature 25