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