Intermittent Exotropia

Dr. Ashraful HuqFCPS

Consultant Bangladesh Eye Trust Hospital

Dhaka, Bangladesh

ExotropiaConstant Exotropia• Infantile Exotropia• Sensory Exotropia• Consecutive Exotropia

Intermittent Exotropia

Fig: Exotropia of Left eye

Intermittent Exotropia•Outward drifting of either eye• Interspersed with periods of good alignment

Fig: Intermittent Exotropia

Most common form of divergent strabismus

Onset before 5 years of age

Manifest during – • Visual inattention• Fatigue• Illness• Daydreaming• Drowsiness upon awakening

CausesImbalance between active

convergence and divergence

Abnormal orbital anatomy

Abnormalities of extraocular muscle proprioception

SymptomsAsymptomatic

Transient diplopia

Asthenopic symptoms

Reflex closure of one eye in bright sunlight

EvaluationHistoryVisual acuityMeasurement of deviationOcular motilitySlit lamp examinationFundoscopyStereoacuity

Cover test in Intermittent Exotropia

Assessing the controlCategory of control of exodeviation

Manifestation of Exodeviation

Fusion resumes

Good control After Cover test Rapidly without blinking /refixating

Fair control After Cover test After blinking /refixating

Poor control Spontaneously Remain manifest

Revised Newcastle Control ScoreHome control (XT or monocular eye closure seen)

0 Never 1 <50% of time fixing in distance2 >50% of time fixing in distance3 >50% of time fixing in distance + seen at near

Clinic control (scored for near and distance fixation)

0 Immediate realignment after dissociation1 Realignment with aid of blink or re-fixation2 Remains manifest after dissociation/prolonged fixation3 Manifest spontaneously

NCS total : n/9

ClassificationBasic :

Same at near and distant fixation

Convergence insufficiency : • Greater at near than at distance• Effects older children and adults

Divergence excess :Greater at distance fixation than at

near

Types-• Simulated divergence excess • True divergence excess

TreatmentTwo types-• Non-surgical• Surgical

Non-surgical TreatmentSpectacle Correction

Overcorrecting minus lens therapy

Part-time patching of dominant eye

Active orthoptic treatment

Base-in prisms

Spectacle correction of refractive error

• Correction of significant myopia, astigmatism and hypermetropia

• Correction of mild myopia

• Mild to moderate degrees of hypermetropia not routinely corrected

Overcorrecting minus lens therapy• Stimulates accommodative

convergence & control exodeviation

• Usually 2-4 D beyond refractive error correction

• Advantage – Promotes fusion & delay surgery

• Disadvantage – Asthenopia

Part-time patching of dominant eye• Converts intermittent exotropia to

phoria

• Done 4 – 6 hours/day

• Advantage – Delays surgical intervention• Disadvantage - Prevents fusion &

accelerate progression

Active orthoptic treatments

• Consist of antisuppression therapy

• Fusional convergence training

• Should be used as supplement to surgery

Prism therapy

• Base-in prism used

• Promotes bifoveal stimulation

• Disadvantage – Causes reduction in fusional vergence amplitude

Indications of Surgical Treatment• Gradual loss of fusional control

• Increased frequency of manifest phase

• Increase size of the basic deviation

• Development of suppression

• Decrease of Stereoacuity

Surgery

• Bilateral lateral rectus recession

• Unilateral lateral rectus recession with ipsilateral medial rectus resection

• Unilateral lateral rectus recession

Fig: (A) Intermittent Exotropia before surgery (B) 3 months after surgery

Lateral rectus recession

Exotropia (PD) LR recession(mm each eye)

20 4.525 5.030 6.035 6.540 7.045 7.550 8.0

LR recession and MR resection

Exotropia (PD) LR recession (mm)

MR resection (mm)

20 4.0 3.025 5.0 4.030 5.5 4.035 6.5 4.540 7.0 4.550 8.0 4.5

Post-operative complications Over Correction :Persistant esotropia 3-4 weeks

after surgery

Treatment - • Correction of refractive error • Part-time alternate patching • Base-out prisms • Botulinum toxin injection• Reoperation

Post-operative complication Under Correction :• Observation

• Orthoptic exercise

• Prism therapy

• Reoperation

Take Home Message • Intermittent Exotropia is difficult to

diagnose

• Proper evaluation required

• Timely treatment necessary

• Follow-up must be done to record progression

• Goal is to restore alignment and preserve Binocular Single Vision