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Prism adaptation

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Prism adaptation

  1. 1. Prism Adaptation <ul><li>∆ correction changes with time </li></ul><ul><li>It appears that ∆ is absorbed </li></ul><ul><li>Is it worth giving ∆? </li></ul><ul><li>Who can be prescribed ∆? </li></ul><ul><li>How can we check who will benefit? </li></ul>
  2. 2. Tonic Vergence <ul><li>Maddox 1893 </li></ul><ul><li>Alpern 1946 </li></ul><ul><li>Ellerbrock 1950 </li></ul><ul><li>Carter 1963 </li></ul><ul><li>Henson and North 1980 </li></ul>
  3. 3. Measuring Adaptation <ul><li>“ Flashed” Maddox Rod </li></ul><ul><li>Measure baseline phoria </li></ul><ul><li>Insert ∆ </li></ul><ul><li>Measure new “phoria” </li></ul><ul><li>Remove ∆ </li></ul><ul><li>Measure new “phoria” </li></ul>
  4. 4. Vertical ∆ Adaptation
  5. 5. Vertical ∆ Adaptation
  6. 6. Distance Horizontal ∆ Adaptation
  7. 7. Distance Horizontal ∆ Adaptation
  8. 8. Near Horizontal ∆ Adaptation
  9. 9. Near Horizontal ∆ Adaptation
  10. 10. Slope Relates to Adaptation
  11. 11. Adaptation
  12. 12. Rate of Adaptation
  13. 13. Amplitude of Adaptation
  14. 14. Amplitude of Adaptation
  15. 15. Symptomatic Patients <ul><li>Patients with BV problems have abnormal adaptation </li></ul><ul><li>Abnormality greatest at distance producing symptoms </li></ul><ul><li>Horizontal & vertical systems are functionally independent </li></ul><ul><li>Poor correlation between phoria, FD, fusional reserves and adaptation </li></ul>
  16. 16. Effect of Age: Convergent
  17. 17. Effect of Age: Divergent
  18. 18. Effect of Age: Convergent
  19. 19. Effect of Age: Divergent
  20. 20. Clinical Assessment <ul><li>Place ∆ before eye </li></ul><ul><li>Allow binocular viewing </li></ul><ul><li>Leave patient for 3 minutes </li></ul><ul><li>Measure phoria </li></ul><ul><li>Compare to baseline measure of phoria </li></ul>
  21. 21. Tonic Vergence <ul><li>Tonic position starting point for all vergence responses </li></ul><ul><li>Additional demand induces shift in starting point </li></ul><ul><li>Fusional effort in each direction altered </li></ul><ul><li>To restore relative balance the tonic position shifts </li></ul>
  22. 22. Model of Adaptation <ul><li>Fast fusional vergence: responds to retinal disparity </li></ul><ul><li>Slow fusional vergence: driven by output of the fast system </li></ul>
  23. 23. Computer Simulation
  24. 24. Model (Schor 1980)
  25. 25. Summary <ul><li>Prism adaptation present in patients </li></ul><ul><li>Mechanism of adaptation related to tonic position </li></ul><ul><li>Vergence system has fast and slow components </li></ul><ul><li>Adaptation different at Distance and Near </li></ul><ul><li>Assess patients prior to giving ∆ </li></ul>

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