Convergence insufficiency

ConvergenceDisjugate simultaneous and synchronous

inward rotation of both eye which results from co-contraction of the two medial rectus muscles

Allows bifoveal single vision maintained at near fixation distance

Does not deteriorate with ageCan be improved by exercises

Unit of measurement

Clinical measurement – Prism Diopter

The amount of convergence is calculated by using the formula: 1/d × IPD where

d is the distance and IPD is interpupillary distance.

Thus, a 6-cm IPD requires 6 dioptres of convergence for a fixation distance of 1 m.

TypesVoluntary convergenceTonic convergence Accommodative Convergence Fusional convergenceProximal convergence

Contd..1.Tonic

due to the tone of the extraocular muscles initiating movement from the anatomical position of rest

2. Accommodativewhich is initiated by the stimulus of accommodation.

Contd..3. Fusional

which is initiated by a fusional stimulus. an involuntary vergence movement to

maintain BSV

4. Proximal induced by the awareness of a near object

One-third of convergence relates to tonic, fusional and proximal convergence.

Two-thirds is accommodative

 NPC value is greater than 10 cm

Convergence insufficiency

Inability of eyes to obtain or maintain adequate binocular convergence

Most common cause of ocular asthenopic symptoms.

First described by von Graefe in 1855 and later elaborated by Duane

one of the most common causes of ocular discomfort

most common cause of muscular asthenopia

Clinical signs of CI1) Exophoria greater at near than at

distance(N>D)

2) A receded near point of convergence

3) Reduced positive fusional vergence at near

4) Low AC/A ratio

5) Little or no lag of accommodation

Symptoms due to muscular fatigue

Eye strain and sensation of tension around globe.

Headache and eye ache after intense near work and relieved when eyes are closed

Difficulty in changing focus from distance to near objects

Itching, burning and soreness of eyes and even hyperemia of nasal half of the conjunctiva

Symptoms due to failure to maintain BSVBlurred vision and crowding of words while

reading

Intermittent crossed diplopia for near under the condition of fatigue

If untreated, in some cases, convergence insufficiency can lead to an outward eye turn that comes and goes intermittent exotropia

Less common complaintsNausea motion sicknessDizziness panoramic headaches gritty sensation in the eyesgeneral fatigue

Aetiology of CIPrimary or idiopathic:

In many cases, exact etiology is not known.

May be associate with:Wide IPDDelayed or inadequate functional developmentGeneral debilityPsychological instabilityOver work or worry

RefractiveAssociated with uncorrected high

hyperopia and myopia

High hyperopes (>5D) usually make no effort to accommodate and there is deficient accommodative convergence.

Myopes may not need accommodation and thus lack accommodative convergence.

Muscular imbalancesExophoria IXTVertical muscle imbalances

Consecutive convergence insufficiency :May occur following either recession of

medial recti or resection of lateral rectus

General physical causesdiseases of endocrine gland (e.g. Mobius’ sign

in thyroid ophthalmopathy).

Psychological causes. include anxiety and neurosis

Clinical featuresClinical problem in patient who does

intense near work.Children with increased school work.Desk workers Computer users

Discomfort usually occurs at the end of the day.

Assessment of NPCThe near point of convergence is assessed

objectively using either a fixation target or the fixation target on the RAF rule

Assessment of PFVBase out motor fusion range is measured to

find out blur, break and recovery

N: 21/30/18

D: 8/10/6

Prism Cover test Assess Latent ocular deviation such as

exophoria at distance and near

Near exophoria greater than distance exophoria

Near exophoria distance orthophoria

Vertical imbalances

Intermittent exotropia

Diagnosis of CIType I: NPC receded or Decreased PFV

Type II: NPC receded or PFV decreased and XP N> XP D

Type III: All the clinical signs present

TreatmentOptical:

Proper refractive correction for any presence of ametropia

Myopes given full correction and hyperopes under corrected to stimulate accommodation

TreatmentThree approachesRelieving symptoms

Base in prismPlus reading glassesDivergence exercises

Improving convergenceBrock stringAperture rule trainerPencil push ups

Increase amplitude of fusional convergenceBI/BO prism flipperSynoptophore

Exercise Physiological

diplopia exercise using stereogram

Diploscope

Training of voluntary convergence

Prism therapy:Base –in prism reading glasses or

bifocals with prism in the lower segment are useful as relieving prism

Relieving prisms and bifocals should be prescribed cautiously in young age

Surgical treatmentAs a last resort, when all other measures

fail.

When it is associated with large exophoria at near.

Medial muscle resection can be performed in one or both eyes.

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