Constant Exotropia

• Exo deviations


  • Exotropia
  • Exophoria
  • Divergence excess
  • Convergence weakness
  • Non-specific
• Primary


  • Secondary
  • Consecutive
  • Constant
  • Intermittent
• Relating to


  • Fixation distance
  • Near exotropia
  • Distance exotropia
  • True
  • Simulated
  • Fusion / accommodation
  • Non-specific
• Risk factors for strabismus

  • Low birth weight - < 2500g
  • Gestational age - < 37 weeks
  • Head circumference at birth - > 37cm = 36% higher risk
  • Exotropia more strongly associated with congenital abnormalities 22% malformations or chromosomal abnormalities
  • Constant Exotropia has also been associated with Schizophrenia – Perhaps a developmental trigger
• Aetiology of exotropia


  • Anomalous position of rest
  • Anatomical
  • AC: A
  • Refractive error
  • Myopia
  • Innervational imbalance
  • Hypertonicity of divergence = divergence excess > distance fixation
  • Convergence insufficiency = convergence weakness > near fixation
  • Hypertonicity of divergence & convergence insufficiency = non-specific (basic exotropia) exotropia near = exotropia distance
• Exotropia - mode of onset


  • Typically exophoria
  • Intermittent exotropia
  • Constant exotropia
  • Rarely constant exotropia from birth (Infantile exotropia)
• Prognosis for exotropia


  • Earlier the onset - less chance of gaining functional outcome
  • Longer duration less favourable outcome
  • Progression to increasing exotropia
  • Decreased tonic convergence with age
  • Development of suppression
  • Reducing accommodation with age
  • Increased divergence of the orbits with age
• Primary Exotropia - Differential diagnosis

  • Early onset (infantile exotropia) < 12 months
  • Late onset - decompensated intermittent exotropia
• Primary Constant Exotropia: Aims

  • Differential Diagnosis

  ? Pathology = secondary strabismus (sensory exotropia)

  ? Previous eso deviation = Consecutive exotropia

  Decompensated exophoria – potential BSV

  ? Any associated neurological condition
• Primary Constant Exotropia: Aims


  • Identify amblyopia

  Determine whether functional or non-functional

  Establish type of correspondence
• Primary Constant Exotropia: Aims

  • If functional - restore BSV

  If non-functional - ? psychosocial problems / socially disabling - improve alignment
• Psychosocial


  It relates to one's psychological development in, and interaction with, a social environment. The individual may not be fully aware of this relationship with his or her environment.
• Primary Constant Exotropia - Investigation

  • VA – amblyopia / need for refractive correction

  CT - constant exotropia for all distance

  OM - A/V pattern, check adduction

  PCT - 1/3m, 6m, far distance - elevation, depression, versions

  Other method of measuring angle may be needed
• Primary Constant Exotropia - Investigation

  • Potential BSV – NC/AC

  Sensory fusion tests

  Suppression

  Diplopia

  Abnormal BSV

  Correct angle ? potential NBSV

  How well established?

  Prism Adaptation
• Primary Constant Exotropia - Potential BSV


  • If suppression or diplopia - correct angle and assess whether potential for normal BSV - HOW?

  If potential BSV - determine its quality

  If no potential BSV - assess risk of diplopia with post-op diplopia test (PODT) or BT

  If abnormal BSV - determine its quality, how well established is it?
• Post-op diplopia test


  Why? How? What are the consequences of the results?
• Potential outcomes of post-op diplopia test

  • Suppresses to 35 PD BI then homonymous diplopia with increasing prisms

  2. Suppresses to 25 PD BI then heteronymous diplopia with prisms to 35PD, homonymous diplopia with prisms ≥40PD

  3. No diplopia with correcting / overcorrecting BI prisms to 60PD
• Primary Constant Exotropia - Management

  • Cyclo refraction - Correct refractive error if appropriate

  Treat amblyopia – if < 8yrs (can try older if dense suppression or potential for BSV)

  No further treatment if small angle, no symptoms, AC patient declines it

  Correct deviation - aim depends on functional or non-functional case
• Primary Constant Exotropia - Management

  • Correct the deviation

  Restore BSV

  Non-functional - Improve alignment – ? undercorrect / overcorrect (PODT)
• Primary Constant Exotropia - Management

  • Surgery

  Unilateral recession lateral rectus + resection of medial rectus

  Bilateral LR recession

  3 muscles – large angle > 40PD
• Surgical Correction


  • Prism adapt pre-op

  PODT

  ? Risk of post-op diplopia

  BT – diagnostically ….. Which muscle?
• Surgical Procedures


  • Lateral rectus recession (weakening)

  Medial rectus resection (strengthening)
• Surgical Dose


  • Amount of surgery
• Primary Constant Exotropia - Management

  • Exercises - correct angle first - functional cases only

  Optical treatment - functional cases or to put back into suppression area

  Prisms

  Lenses

  Botulinum toxin - therapeutically
• Exotropia - Botulinum Toxin


  • Inject which muscle?

  What does it do?

  How long does it last?

  What are the side effects?
• Ten patients with constant exotropia - all had no pre-operative evidence of BSV. Post-operatively 9/10 demonstrated fusion.
• Summary


  • Onset – early or late

  Exclude pathology or other neurological disease

  Treat amblyopia

  Investigate sensory status – potential BSV/ correspondence

  If potential BSV - aim to restore

  If no potential BSV – PODT

  Plan appropriate alignment if required