Download - Vergence
The Vergence System
Eye Movements
Postural eye movements
Psycho optical eye movementsFixation; Pursuit; Vergence
Vergence Eye Movements
A disjunctive movement of the eyes that changes the angle formed by the visual axes
Vergence Eye Movements
Convergence and divergence are terms found in the literature
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
NPC
Unit of Measurement
Metre Angle (MA)1D of accommodation
equivalent to 1MA of convergence
Metre Angle
Metre Angle
∆ = MA X PD(cm)Fixation at 33cm for patient with
PD of 60mm∆ = 3 x 6 = 18∆
Vergence
Voluntary
Reflex
Reflex Vergence (Maddox)
TonicAccommodativeProximalFusionalTotal = T+A+P+F
Tonic Vergence
Anatomical position of rest
Physiological position of rest
Accommodative Convergence
Muller 1826Minus lens stimulate
accommodation and caused a vergence response in covered eye
AC/A ratio
Accommodative Convergence
Accommodative Convergence
AC/A Ratio
1D of accommodation for 1MA of convergence?
PD 60mm; Target 33cm; 18∆ convergenceAC/A = 18/3 = 6:1
AC/A Distribution
AC/A Ratio
This is NOT foundAccommodation not accurate?
Accommodation Response
0
1
2
3
4
5
6
7
8
0 1 2 3 4 5 6 7
Unit ratioResponse
Proximal Vergence
Awareness of near objectInstrument accommodation Instrument vergence
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
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
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