Tests of binocularity

these slides describe the different techniques of binocularity examination and its clinical implication

1. Dr Anuradha Chandra Tests of binocularity

2. Binocular vision A large part of our brain is devoted to understanding visual cues Depth information can help us to understand spatial relationships in complex data set

3. Binocular Vision Our two eyes produce a single image in the brain – a “Cyclopean image” Creatures with binocular vision generally have forward-facing eyes that move together.

4. Oculocentric Visual Direction The visual direction of an object can be represented by a line that joins the object and the fovea called the Principal Visual Direction or visual axis. Based on the principal visual direction, the direction of all other objects in the subjects visual field is determined

5. Common visual directon

6. Egocentric Visual Direction Egocentric direction is determined by retinal position, proprioceptive information about the eye, head and body position and the vestibular apparatus. All this information allows us to determine if a change in retinal position is due to object movement or due to eye or head movement Refers to the direction of an object in space relative to one self, rather than the eyes.

7. Retinal correspondence Corresponding retinal points- same visual direction. Non-corresponding points (Disparate points) - different visual directions.

8. Retinal rivalry When dissimilar contours are presented to corresponding retinal areas , fusion becomes impossible and retinal rivalry ensues and gives rise to conflict and confusion. It is explained by presence of separate channels for right and left eyes that compete for access to visual cortex.

9. Theories of binocular vision Correspondence and disparity When disparate retinal points are stimulated by one object point, diplopia occurs. However if horizontal disparity remains within limit of pannums area , a single visual impression with quality of stereopsis is elicited.

10. Theories of binocular vision (contd.) Neurophysiological theory Hubel and Wiesel work gave rise to the theory in which the neurophysiological basis of binocular vision was discovered. They identified cells described as being sensitive to binocular depth in area 18 of the macaque cortex.

11. Physiological diplopia Disparate points give rise to physiological diplopia (double vision).

12. For an object closer than the fixation point crossed diplopia occurs as the point is imaged on the temporal retina of both eyes. The image in the left eye is seen on the right side. Using the cyclopean eye, crossed and uncrossed diplopia can be explored

13. For an object located further than the fixation point, the image of the object falls on the nasal retina of both eyes producing uncrossed diplopia . This is termed uncrossed diplopia because the image in the left eye is seen on the left side

14. The Vieth-Muller circle The Vieth-Muller circle is a theoretical horopter All points on this circle should stimulate corresponding points on the retina and lead to single vision, provided that the fixation point lies on the centre of the circle and the eyes rotate about its nodal point (instead of their centre of rotation). The Vieth-Muller circle assumes there is angular symmetry of the corresponding points .

15. The Vieth-Müller circle (theoretical horopter) is based on certain geometric assumptions about the eyes. These are: Each retina may be represented by a perfect circle. Corresponding points are evenly space across the nasal and temporal retinas of each eye. • Both retinas are the same size and corresponding points are perfectly matched for their locations in the two eyes. An horopter measured on the basis of human visual observiations differs slightly from the Vieth-Müller circle and is referred to as an empirical horopter.

16. Pannums area Within a small distance, either side of the horopter, objects can still be fused and seen as single. Strictly speaking, they fall on non-corresponding retinal points and there will be a small disparity. The zone on either side of them horopter within which it is still possible to see objects singly is known as Panum’s area. Panum’s area does not have a fixed size but varies depending on stimulus conditions, being larger for big, moving objects, but is narrower for detailed and stationary objects.

17. Human Interpupillary Distance (IPD) Need separation between our eyes to see in stereo mean adult IPD is around 63 mm Vast majority of adults have IPDs in the range 50– 75 mm Wider range of 45–80 mm is likely to include (almost) all adultsand the minimum IPD for children (down to five years old) is around 40 mm

18. Binocular Vision Our eyes are separated by about 6.5 cm so our retinas each get a slightly different view of the world The right actually sees more distance between the objects (as well as slightly different parts of the surfaces)

19. Field of binocular vision

20. INVESTIGATIONS FOR BINOCULAR VISION All the tests are aimed at assessing the presence or absence of: Simultaneous perception Fusion with some amplitude Stereopsis Normal or abnormal retinal correspondence Suppression

21. Tests for detection:- Worth 4 dot test 4D base out prism test Red glass test Bagolini striated lens test Vectographic test Synoptophore test

22. Sensory tests Diplopia tests Most dissociating Maddox rod Dark red filter Worth 4 dot with room lights out Least dissociating Bagolini striated lenses

23. Maddox rod test

24. Red filter test :- Place red glass over one eye and fixate on a single light source Patients with orthotropia and NRC will see one pinkish red light Esotropia with NRC causes uncrossed diplopia and EXT causes crossed diplopia, neutralization of deviation causes disappearance of diplopia

25. Patient with ARC will also see one light even in presence of squint, neutralization of deviation causes diplopia Patient with suppression will see only one light, white or red Patient with alternate fixation will see alternately red and white light Test can be made more dissociating by using denser red color or turning down the lights

26. Red filter test in NRC and ARC

27. Red filter test in patient with RE suppression

28. Worth Four Dot Test Utilizes red-green color dissociation . box containing four panes of glass, arranged in diamond formation, which are illuminated internally- 2 green , 1 red and 1 white . red and green goggles distance (6m)and near vision(33cm)

29. The patient sees all the four dots. normal binocular response with no manifest deviation - NRC with no heterotropia ) with manifest squint - Harmonious ARC The patient sees five dots. red dots appear to the right - uncrossed diplopia with esotropia red dots appear to the left of the green dots - crossed diplopia with exotropia The patient sees three green dots - suppression of right eye. The patient sees two red dots - suppression of left eye.

30. Bagolini's Striated Glasses Test Micro Maddox cylinders 45 degree OS 135 degree OD Non - refractive

31. Interpretation Crossing of the lines at right angles to each other If cover test reveals no shift and fixation is central, the patient has NRC If cover test reveals a shift, harmonious ARC is present Foveal suppression scotoma (fixation point scotoma) with peripheral fusion if no shift occurs with cover test, NRC exists, if shift occurs, ARC exists Single line represents suppression

32. Synaptophore

33. Before any test is undertaken it is essential to assess the: visual acuity fixation in the squinting eye direction and size of deviation

34. SIMULTANEOUS MACULAR PERCEPTION This is the most elementary type of binocularity and is tested with the help of SMP slides on the synaptophore, which depicts objects which are dissimilar, but mutually agnostic (e.g. presenting a picture of a square to one eye and a circle to other). The commonly used slides are bird and cage, lion and cage, butterfly and net .

35. If superimposition occurs, it is necessary to make a more accurate assessment by using target slides of different sizes. Simultaneous foveal perception slide – subtend an angle of 1 degree at the nodal point Simultaneous parafoveal perception slides – subtend angle of 1-3 degree Simultaneous paramacular perception slides – subtend angle of 3-5 degree Simultaneous peripheral perception slides – subtend angle greater than 5 degrees

36. The term simultaneous perception does not necessarily mean bifoveal fixation as it can also occur in ARC. It merely indicates the presence or absence of suppression. This term is erroneous as it embraces both foveal and parafoveal perception in the same definition .

37. Tests for Fusion Fusion is demonstrated by using slides in which similar pictures with different controls are presented to the eyes simultaneously e.g. letter L and F fused into E, rabbit with a tail and rabbit with flower in hand, fused into one rabbit having tail and flower

38. Normal fusion amplitudes are: A) Horizontal vergences: Convergence→ 35 ∆ to 40 ∆ Divergence → 5 ∆ to 7 ∆ B) Vertical vergence: Supravergence→3 ∆ Infravergence→3 ∆ C) Cyclovergence →2-3 ∆

39. Tests for stereoacuity Synatophore-with slides TNO TEST-using red-green glass Randot’s &Titmus stereotest Lang’s test-no glasses Special 3D pictures Stereogram Major amblyoscope Two pencill test

40. Randot stereo test Most popular test The peripheral dot distribution are identical Central dots of each slide shifted horizontally,so the horizontal disparity cause stereopsis. With polaroid glass,at distance of 40cm It test Near binocular vision

41. Randot test

42. The wirt’s circles 1-10 test the stereoacuity from 400arc sec to 20arc sec. It misses myopes of -3D at screening Its not a real test of biological function as more than 40% child shows less than 40 arc response

43. RANDOT E test

44. TNO anaglyph test

45. It use Randot back ground and red-green glass to dissociate two images Adv—elicit quantitative response without changing testing distance. Range-15arc to 480 arc

46. LANG’S TEST-I

47. L ANG STEREOTEST 1: A simple test is designed for stereopsis training in children based on two principles, random dots and cylinder gratings. In binocular vision stereoscopic shapes are recognised . No glasses are required meaning the patients eye movements are easily observed. Comes in wallet (car, cat and star shapes)

48. Distance stereo acuity tests

49. Two pencil test It’s a gross test Two rod or pencil should approach , horizontallly It measures grossly near 400sec of arc disparity

50. Thanks for Listening