1. Binocular Vision, Fusion, and Accommodation

2. Fusion Development in the Infant
Birth – fixation reflex poor with random eye movements
2-3 weeks – follows light monocularly
6 weeks to 6 months – follows light binocularly
4 weeks to 6 months – convergence developing
By 6 months – accommodation developing – lags behind convergence

3. Fusion
Sensory fusion – the cortical process of blending the images from each eye into a single binocular stereoscopic image
Motor fusion – the mechanism that allows fine-tuning of eye position to maintain eye alignment – this is known as fusional vergence

5. Approximately 70% of the cells in the striate cortex are binocular cells
Retinal areas from each eye that project to the same binocular cortical cells are called corresponding retinal points.

7. Worth’s Three Degrees of Fusion
Simultaneous perception
Flat fusion
Stereopsis

8. Simultaneous perception

9. Flat Fusion
Worth Four Dot Test

10. Stereopsis
Titmus Stereo Test

11. Binocular Single Vision
Separate and slightly dissimilar images arising in each eye are fused together as a single image.

12. Advantages of Binocular Vision
Single Vision
Stereopsis
Enlargement of visual field
Compensation for blind spot and other differences in the field of vision

13. Normal Binocular Single Vision Requirements
Clear visual axis
Sensory fusion
Motor fusion

14. Sensory Obstacles
Dioptric obstacles – refractive errors, anisometropia
Prolonged monocular activity – severe ptosis, media opacities
Retinoneural – lesions of retina, optic nerve
Proprioceptive

15. Motor Obstacles Congenital craniofacial malformations
Conditions affecting extraocular muscles
CNS lesions – involving upper motor neurons

16. The Perception of Depth
Stereopsis
Monocular clues to depth

17. Monocular Clues to Depth
Relative size
Interposition
Linear perspective
Aerial perspective
Light and shade
Motion parallax

23. Visual Direction
Local sign – positional information transferred from the retina to the motor system – the fovea has a retinomotor value of zero
Retinal correspondence = single vision
Retinal disparity = diplopia

24. Oculocentric Visual Direction

25. Egocentric Visual Direction

26. Cyclopean Eye

27. The Perception of Space
Retinal corresponding points
Horopter
Retinal disparity
Panum’s fusional area
Physiological diplopia

28. The Horopter
Vieth-Muller Circle
Empirical Horopter

29. The Horopter

31. Normal binocular single vision – the images of the fixated object are bifoveal with no manifest deviation of the eyes
Anomalous binocular single vision – the images of the fixated object are projected from the fovea of one eye and an extrafoveal position in the other eye – there is a small manifest deviation of the eyes

32. Misalignment of the two eyes can lead to diplopia and confusion
Diplopia – occurs when one object is seen in two places
Confusion – occurs when two dissimilar objects are seen in the same place

33. Suppression and Retinal Rivalry
Normal – physiological diplopia – also known as suspension
Anomalous – pathological diplopia and confusion – cortical inhibition of suppressed eye
Retinal or binocular rivalry – rapid alternation of dissimilar images

34. Testing Retinal Correspondence
Bagolini lenses
Red filter test
Worth four dot test
Hering-Bielschowsky afterimage test
Foveo-foveal test of Cuppers

37. Worth Four Dot Test

38. Testing Suppression Worth four dot test Polaroid vis-à-vis test
Amsler grid
4 prism diopter base out test
Red filter test
Bagolini lenses

39. Polaroid Tests

40. Amsler Grid

41. Versions – conjunctive eye movements – the two eyes move in the same direction
Pursuits
Saccades

42. Vergences – disconjunctive eye movements – the eyes move in opposite directions
Convergence
Divergence
Vertical vergence

43. Vergence
Tonic
Proximal
Fusional
Accommodative

44. Accommodation
Tonic – in the absence of a visual stimulus, the accommodation adopts an intermediate position of D
Proximal – resulting from apparent nearness of an object
Convergence – accommodation linked to convergence
Reflex – involuntary response to blur to maintain a clear image
Voluntary – not dependent on a stimulus