Download - Vergence
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The Vergence System
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Eye Movements
Postural eye movements
Psycho optical eye movementsFixation; Pursuit; Vergence
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Vergence Eye Movements
A disjunctive movement of the eyes that changes the angle formed by the visual axes
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Vergence Eye Movements
Convergence and divergence are terms found in the literature
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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
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NPC
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Unit of Measurement
Metre Angle (MA)1D of accommodation
equivalent to 1MA of convergence
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Metre Angle
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Metre Angle
∆ = MA X PD(cm)Fixation at 33cm for patient with
PD of 60mm∆ = 3 x 6 = 18∆
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Vergence
Voluntary
Reflex
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Reflex Vergence (Maddox)
TonicAccommodativeProximalFusionalTotal = T+A+P+F
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Tonic Vergence
Anatomical position of rest
Physiological position of rest
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Accommodative Convergence
Muller 1826Minus lens stimulate
accommodation and caused a vergence response in covered eye
AC/A ratio
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Accommodative Convergence
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Accommodative Convergence
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AC/A Ratio
1D of accommodation for 1MA of convergence?
PD 60mm; Target 33cm; 18∆ convergenceAC/A = 18/3 = 6:1
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AC/A Distribution
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AC/A Ratio
This is NOT foundAccommodation not accurate?
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Accommodation Response
0
1
2
3
4
5
6
7
8
0 1 2 3 4 5 6 7
Unit ratioResponse
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Proximal Vergence
Awareness of near objectInstrument accommodation Instrument vergence
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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
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Heterophoria
Alignment maintained by fusion reflexSuspend fusion and eyes adopt “fusion
free” positionError of alignment is called a heterophoriaPhoria is a measure of error between
desired alignment and position resulting from proximal, tonic and accommodative components
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Summary
Vergence highest order eye movementProblems of vergence lead to symptomsManagement of BV problems needs
understanding of vergence systemTotal vergence response made up from
Tonic, Proximal, Accommodative and Fusional
Consider balance of components