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