Measurement of Convergence

Measurement of Convergence

It is essential that assessment of vergence is made during an eye examination

There are many aspects to the vergence response

Near Point of Convergence (NPC)

NPC

Subjective NPC: Patient reports diplopia

Objective NPC: Clinician observes point when one eye turns out

NPC

Less than 12cm is normalBetween 12 and 15cm is suspectGreater than 15cm is

anomalous: orthoptic training is indicated

Jump Vergence

A more natural testPatient changes fixation from

distance to nearIf task is difficult patient will

attempt to look away

Fusional Vergence

Phorias are kept latent by the fusion reflex

Large phorias may need a large fusional effort to maintain binocularity

Important to know how much fusional vergence is being used

Positive Fusional Reserves

Negative Fusional Reserves

Measurements

Break Point

Recovery Point

Blur Point

Base In

Base Out

Relative Vergence

When eyes converge accommodation is stimulated

The target will become blurredThe amount of ∆ to the blur

point is known as the relative convergence

Relative Vergence

Negative Relative Convergence: amount of BI ∆ to blur

Positive Relative Convergence: amount of BO ∆ to blur

Vertical Fusional Reserves

Measured with Base up or down ∆

Fusional range small

Normal Values

Clinical Value

Distance phoria: 8XOPPositive reserve: 16 ∆Total +ve vergence: 8 + 16 =241/3 of total being used to over

come phoria

Accommodation and Vergence

Relative Accommodation

Amount of accommodation which can be exerted while vergence remains constant

Measured by using +ve and -ve lenses

Zone of Clear Vision

Zone of Clear Vision

Zone of Clear Vision

Summary

Consider all aspects of vergenceNPC a routine measurePhoria a routine measureFusional reserves should be

considered in diagnosis and management of BV problems