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Normally when a target moves from far-to-near, our vision benefits E from linking accommodation and convergence. The Near Triad AC/A AND CA/C E E JEN SIMONSON, OD, FCOVD EE

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1.Our eyes accommodate to see clearly at near. The amount of accommodative convergence (AC) 2. The accommodation also drives convergence to see single driven by the amount of accommodation (A) is vision at near. called the AC/A ratio. E E

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1.Accommodation 1.Accommodation

E E E E

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1.Accommodation 1.Accommodation 2.Convergence 2.Convergence E

E E EE

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1.Accommodation 2.Convergence E

E E 1.Accommodation EE 2.Convergence 3.Pupil Constriction

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How does the visual system respond to a minus lens?

All three E neuro- muscular responses occur with a stimulus moving from far to E E near.

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Step 1: Minus lenses Minus lenses stimulate accommodation. Through the AC/A, the eyes reflexively converge. This creates the situation where our eyes cause defocus, which must adjust by diverging to keep the image clear and single. stimulates E accommodation. E

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When the eyes Step 2: Convergence is accommodate to stimulated when the match the lens E eyes accommodate. E power, the target This creates double becomes clear. vision.

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EE

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Step 3: Fusional Divergence realigns Step 1: To clear a plus the eyes to the E E lens, the eyes must image. Now vision is relax accommodation. clear and single.

E E E E EE EE

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Step 2: This When the eyes adjust relaxation of focus E to match the lens also causes a E power, the target relaxation of becomes clear. vergence – the eyes diverge.

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EE

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Step 3: We must 1.Accommodation E use fusional 2.Convergence convergence to 3.Pupil Constriction create single vision.

E E

EE

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The work of Linda Sanet, COVT: The work of Linda Sanet, COVT:

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Stimulating Accommodation Stimulating more makes the Accommodation also eyes converge more. stimulates This is because when Convergence. an object moves closer, the eye has to This is called the both focus more and E “AC/A” E turn in more. The AC/A is the amount of Accommodative Convergence per unit of Accommodation.

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E E

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Stimulating Convergence more makes the eyes When an object accommodate more. This is moves from near because when an object to far, the moves closer, the eye has to E response is both turn in more and focus relaxed more. accommodation, divergence and pupil dilation. E E EEE

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A plus lens will stimulate relaxation When we add a of accommodation lens or prism in and divergence front of the eye, through the AC/A. we still respond We must then use as if the target fusional convergence moved closer or to see single vision. further away. We must then make an adjustment to see clear and single vision.

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A minus lens A base-in (apex- stimulates out) prism accommodation. stimulates Through the AC/A, divergence. the eye also Through the CA/C, converges. We must the eye also relaxes then adjust by focus. We must fusional divergence then adjust by to maintain single focusing to vision. maintain clear 5 vision. BI

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A base-out (apex-in) prism stimulates The more you accommodate (focus), the more the convergence. Through the CA/C, eyes converge. The more you converge, the more 5 the eye also your eyes focus. BO accommodates. We must then adjust by E relaxing accommodation to maintain clear vision. E E E

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How lenses and prisms How lenses and prisms affect affect eye alignment eye alignment and focus: and focus: Plus and Minus lenses cause defocus – the first eye response will be to clear the image. The second response is reflexive, the vergence will change. Lastly the eyes will have to realign. E E

Base-in and Base-out prisms cause disparity – the first eye response will be to fuse the image. The second response is E E reflexive, the focus will change. Lastly the eyes will have to refocus.

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How does the visual system Option #1 – it does NOT respond. respond to a Base-out Prism? The image is blurry and double.

E E E E

EE EE

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Base-Out Prism stimulate convergence. Through the CA/C, the eyes Step 1: Base-out reflexively accommodate. This creates the situation where our eyes E Prism stimulates must adjust by relaxing focus to keep the image clear and single. convergence to keep the target single.

E E E E

EE EE

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Step 2: Convergence stimulates Step 3: The eyes must relax focus to clear the accommodation, E image. E which makes the target look blurry.

E E E E

E E

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When the eyes Step 1: Base-in Prism divergence to E requires divergence to match the new E keep the target single. image position, the target becomes single.

E E E E

EE EE

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Step 2: Divergence creates a relaxation Step 3: The eyes of accommodation, E E which makes the accommodate to make target look blurry. the image clear.

E E E E

E E

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1. Relax focus to clear the 1. Increase focus to clear image. the image. 2. Eyes reflexively 2. Eyes reflexively diverge. converge. 3. Converge eyes to 3. Diverge eyes to regain regain single vision. single vision.

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1. Diverge to fuse the 1. Converge to fuse the image. image. 5 2. Eyes reflexively relax 2. Eyes reflexively focus. BO focus. 3. Relax 3. Accommodate to accommodation to 5 regain clear vision. BI regain clear vision.

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