ORTH 140 NORMAL BINOCULAR SINGLE VISION AND MOTOR FUSION Academic Year 2013-14 Gail Stephenson

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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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

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

ACCOMMODATIVE VERGENCE SYSTEM Stimulus is a blurred image

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

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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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

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

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)

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.

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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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

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

MOTOR FUSION This can be measured using the Synoptophore or Prisms

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

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

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

RISLEY PRISM

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.

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

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

CONTROLS EITHER WITHIN THE FRAMEWORK OF THE PICTURE – CENTRAL CONTROLS

CONTROLS EITHER OUTSIDE THE FRAMEWORK OF THE PICTURE – PERIPHERAL CONTROLS

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

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

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

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