1. ORTH 140 NORMAL BINOCULAR SINGLE VISION AND MOTOR FUSION
Academic Year
Gail Stephenson

2. SENSORY FUSION Definition
The neural process by which images in each retina are synthesized or integrated into a single percept. In normal BV, this process occurs when corresponding regions of the retina are stimulated.
This is a cortical action

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4. FUSION Real life eyes not still
Need to fuse far away, then near to you
Need to fuse to the left and then to the right.
Eyes need to move so that images fall on corresponding points
Ability to maintain fusion at different distances – MOTOR FUSION

5. MOTOR FUSION
This adapting mechanism also helps you to compensate for any tendency for the yes to deviate –
LATENT DEVIATION
PHORIAS

6. ACCOMMODATIVE VERGENCE SYSTEM
Stimulus is a blurred image

7. PROXIMAL VERGENCE SYSTEM
Psychological
Awareness of nearness induces convergence – proximal convergence

8. If the images fall on the fovea or up to 2 degrees around the fovea this is known as
CENTRAL FUSION
FUSION can also occur when the images project onto the peripheral portions of the retinas
PERIPHERAL FUSION

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11. INVESTIGATION OF SENSORY FUSION
Different images to either eye and evaluate how the patient perceives
An accurate diagnosis relies on the results of several tests
A good Orthoptic Report relies on the ability of the Orthoptist to add things together

12. INVESTIGATION OF SENSORY FUSION
Worth’s Lights
Bagolini Glasses
Bagolini Filter Bar
Neutral Density Filter Bar
Controlled Binocular Acuity

13. CONTROLLED BINOCULAR ACUITY
If patient appears to have no manifest deviation
Patient reads down the chart maintaining Binocular Vision
No dissociation
The smaller the letter the harder to fuse
If patient maintains Binocular Vision good sensory fusion
Was known as Binocular Visual Acuity (BVA) Now known as Controlled Binocular Acuity(Davis & Firth 2008)

14. MOTOR FUSION
Motor Fusion is when the eyes move until the object of regard falls on corresponding retinal points (e.g. Foveas) in response to disparate retinal stimuli
Motor fusion can be reflex.

15. FUSION REFLEX
In a person with BSV, when an image is displaced from the fovea of one eye (disparate retinal stimulus) the brain causes the eye to rotate to re-fixate the target on the retina
Hering’s Law causes
the other eye to make a conjugate movement, this results in
Diplopia
The brain’s desire for BSV causes the second eye to re- adduct to restore bifoveal fusion

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21. MOTOR FUSION
Motor fusion allows the subject to maintain single vision during disjugate eye movements. (and all movements of the 2 eyes)
Motor Fusion can compensate for latent deviations

22. MOTOR FUSION If the patient has a latent convergence Esophoria
Eyes need to diverge to control this.
If the patient has a latent divergence
Exophoria
Eyes need to converge to control this

23. MOTOR FUSION
This can be measured using the Synoptophore or Prisms

24. MOTOR FUSION
Step like change in fusion –
PHASIC
Smooth change –
TONIC

27. MOTOR FUSION
Fusion can be assessed Horizontally, Vertically or Cyclovertically
The Synoptophore measures all 3 ranges

29. PRISMS Prisms can assess Horizontal and Vertical Fusion Ranges
A Prism Bar assesses
Phasic Fusion
A Risley Prism or synoptophore assesses
Tonic Fusion

32. RISLEY PRISM

34. FUSION RANGE
This is the range of disjugate movements (convergence and divergence or elevation and depression), the patient can make whilst maintaining Binocular Single Vision.
The larger the range the more ability the patient has to compensate for use of the eyes in all positions.

35. FUSION RANGE Need to ensure that binocular vision is maintained.
If a control stimulus is provided to either eye orthoptist can ensure range is binocular.
MUST use smallest size target relating to the patients VA

36. CONTROLS Using the synoptophore
Each one of a pair of slides has features not found on the other slide

37. CONTROLS EITHER WITHIN THE FRAMEWORK OF THE PICTURE – CENTRAL CONTROLS

38. CONTROLS EITHER OUTSIDE THE FRAMEWORK OF THE PICTURE – PERIPHERAL CONTROLS

39. CONTROLS
Using Prisms
Using the Bagolini Lenses and a light provides an additional different image to either eye.

41. FUSION RANGE The fusion ability is influenced by the size of the image
The larger the image the easier it is to fuse

43. POSSIBLE QUESTION ON THIS TOPIC
List all the tests you could use to assess BV
Identify those that involve:
Directional Sensitivity
Retinal Correspondence
Motor Fusion
Sensory Fusion
Phasic Fusion
Tonic Fusion
Central Fusion
Peripheral Fusion

44. Possible questions on the 5 Lectures
Should be able to label diagrams of :-
Directional Sensitivity
Physiological Diplopia
Retinal Correspondence
Definitions of all grades of Binocular Vision