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Vergence

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Vergence

  1. 1. The Vergence System
  2. 2. Eye Movements <ul><li>Postural eye movements </li></ul><ul><li>Psycho optical eye movements </li></ul><ul><ul><li>Fixation; Pursuit; Vergence </li></ul></ul>
  3. 3. Vergence Eye Movements <ul><li>A disjunctive movement of the eyes that changes the angle formed by the visual axes </li></ul>
  4. 4. Vergence Eye Movements <ul><li>Convergence and divergence are terms found in the literature </li></ul>
  5. 5. Near Point of Convergence <ul><li>The closest point to which the eyes can be converged whilst retaining bifoveal fixation </li></ul><ul><li>A normal NPC would be between 8cm-12cm </li></ul>
  6. 6. NPC
  7. 7. Unit of Measurement <ul><li>Metre Angle (MA) </li></ul><ul><li>1D of accommodation equivalent to 1MA of convergence </li></ul>
  8. 8. Metre Angle
  9. 9. Metre Angle <ul><li>∆ = MA X PD(cm) </li></ul><ul><li>Fixation at 33cm for patient with PD of 60mm </li></ul><ul><li>∆ = 3 x 6 = 18∆ </li></ul>
  10. 10. Vergence <ul><li>Voluntary </li></ul><ul><li>Reflex </li></ul>
  11. 11. Reflex Vergence (Maddox) <ul><li>Tonic </li></ul><ul><li>Accommodative </li></ul><ul><li>Proximal </li></ul><ul><li>Fusional </li></ul><ul><li>Total = T+A+P+F </li></ul>
  12. 12. Tonic Vergence <ul><li>Anatomical position of rest </li></ul><ul><li>Physiological position of rest </li></ul>
  13. 13. Accommodative Convergence <ul><li>Muller 1826 </li></ul><ul><li>Minus lens stimulate accommodation and caused a vergence response in covered eye </li></ul><ul><li>AC/A ratio </li></ul>
  14. 14. Accommodative Convergence
  15. 15. Accommodative Convergence
  16. 16. AC/A Ratio <ul><li>1D of accommodation for 1MA of convergence? </li></ul><ul><li>PD 60mm; Target 33cm; </li></ul><ul><li>18∆ convergence </li></ul><ul><li>AC/A = 18/3 = 6:1 </li></ul>
  17. 17. AC/A Distribution
  18. 18. AC/A Ratio <ul><li>This is NOT found </li></ul><ul><li>Accommodation not accurate? </li></ul>
  19. 19. Accommodation Response
  20. 20. Proximal Vergence <ul><li>Awareness of near object </li></ul><ul><li>Instrument accommodation </li></ul><ul><li>Instrument vergence </li></ul>
  21. 21. Fusional Vergence <ul><li>Corrects any residual error from other components </li></ul><ul><li>Effort can cause patient to experience symptoms </li></ul><ul><li>Important that fusional effort is within middle third of total range </li></ul>
  22. 22. Heterophoria <ul><li>Alignment maintained by fusion reflex </li></ul><ul><li>Suspend fusion and eyes adopt “fusion free” position </li></ul><ul><li>Error of alignment is called a heterophoria </li></ul><ul><li>Phoria is a measure of error between desired alignment and position resulting from proximal, tonic and accommodative components </li></ul>
  23. 23. Summary <ul><li>Vergence highest order eye movement </li></ul><ul><li>Problems of vergence lead to symptoms </li></ul><ul><li>Management of BV problems needs understanding of vergence system </li></ul><ul><li>Total vergence response made up from Tonic, Proximal, Accommodative and Fusional </li></ul><ul><li>Consider balance of components </li></ul>

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