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The Near Triad AC/A and CA/C E E JEN SIMONSON, OD, FCOVD EE

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The Near Triad AC/A and CA/C E E JEN SIMONSON, OD, FCOVD EE 4/23/2017 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 THE NEAR TRIAD 1 THE NEAR TRIAD 2 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 E E E E EEE E THE NEAR TRIAD 3 THE NEAR TRIAD 4 1.Accommodation 1.Accommodation E E E E THE NEAR TRIAD 5 THE NEAR TRIAD 6 1 4/23/2017 1.Accommodation 1.Accommodation 2.Convergence 2.Convergence E E E EE THE NEAR TRIAD 7 THE NEAR TRIAD 8 1.Accommodation 2.Convergence E E E 1.Accommodation EE 2.Convergence 3.Pupil Constriction THE NEAR TRIAD 9 THE NEAR TRIAD 10 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. THE NEAR TRIAD 11 THE NEAR TRIAD 12 2 4/23/2017 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 E E E E EE THE NEAR TRIAD 13 THE NEAR TRIAD 14 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. E E E E EE THE NEAR TRIAD 15 THE NEAR TRIAD 16 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 THE NEAR TRIAD 17 THE NEAR TRIAD 18 3 4/23/2017 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. E E E E EE THE NEAR TRIAD 19 THE NEAR TRIAD 20 Step 3: We must 1.Accommodation E use fusional 2.Convergence convergence to 3.Pupil Constriction create single vision. E E EE THE NEAR TRIAD 21 THE NEAR TRIAD 22 The work of Linda Sanet, COVT: The work of Linda Sanet, COVT: THE NEAR TRIAD 23 THE NEAR TRIAD 24 4 4/23/2017 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. THE NEAR TRIAD 25 THE NEAR TRIAD 26 E E E E E E EE EEE THE NEAR TRIAD 27 THE NEAR TRIAD 28 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 THE NEAR TRIAD 29 THE NEAR TRIAD 30 5 4/23/2017 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. THE NEAR TRIAD 31 THE NEAR TRIAD 32 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 THE NEAR TRIAD 33 THE NEAR TRIAD 34 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 THE NEAR TRIAD 35 THE NEAR TRIAD 36 6 4/23/2017 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. THE NEAR TRIAD 37 THE NEAR TRIAD 38 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 THE NEAR TRIAD 39 THE NEAR TRIAD 40 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 THE NEAR TRIAD 41 THE NEAR TRIAD 42 7 4/23/2017 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 THE NEAR TRIAD 43 THE NEAR TRIAD 44 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 THE NEAR TRIAD 45 THE NEAR TRIAD 46 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 THE NEAR TRIAD 47 THE NEAR TRIAD 48 8 4/23/2017 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. THE NEAR TRIAD 49 THE NEAR TRIAD 50 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. THE NEAR TRIAD 51 THE NEAR TRIAD 52 9.
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