What is exotropia?

What is Exotropia?

Exotropia is an outward deviation of one or both eyes, representing a form of strabismus (binocular misalignment) where the visual axes diverge. 1 This condition is characterized by one eye turning outward while the other maintains normal alignment, particularly when viewing distant objects.

Types and Classification

Exotropia can be categorized based on several factors:

1. Frequency of deviation:

   • Intermittent exotropia (IXT): The most common form, where the eye turns outward only occasionally, typically when the patient is tired, ill, or inattentive 2
   • Constant exotropia: The eye remains turned outward at all times

2. Age of onset:

   • Infantile exotropia: Presents before 1 year of age (relatively rare in healthy children) 3
   • Childhood-onset exotropia: Typically appears before 3 years but may be detected later 1

3. Clinical presentation:

   • Intermittent exotropia: Typically appears before 3 years, with deviation becoming manifest during fatigue, visual inattention, or illness 1
   • Convergence insufficiency: Characterized by exotropia at near fixation, reduced fusional convergence, and remote near point of convergence 1
   • Sensory exotropia: Associated with unilateral or bilateral vision loss 1
   • Consecutive exotropia: Occurs after surgery for esotropia 1

Epidemiology and Risk Factors

• Exotropia occurs in approximately 1% of the population 1
• Risk factors include:
  • Prematurity
  • Perinatal morbidity
  • Genetic disorders
  • Maternal substance abuse and smoking during pregnancy
  • Family history of strabismus
  • Female sex (twice as frequent in girls than boys)
  • Refractive errors (astigmatism, myopia, anisometropia) 1
  • Hypoxia at birth 4

Clinical Features

Patients with exotropia may present with:

• Outward deviation of one eye, particularly noticeable when looking at distant objects
• Eye closing or covering in bright light (common in intermittent exotropia)
• Suppression of the image from the deviated eye (patients typically don't report diplopia)
• Mild amblyopia in some cases (severe amblyopia is uncommon in intermittent exotropia) 1
• Asthenopic symptoms (eye strain, fatigue) with near work in convergence insufficiency 1
• Reduced quality of life and negative impact on self-image 1

Natural History

The natural course of exotropia varies:

• Some patients with intermittent exotropia remain stable or spontaneously improve without treatment
• Others show deterioration over time with:
  • Increased angle of deviation
  • Decreased fusional control
  • Development of suppression 1, 5
• A small proportion eventually develop constant exotropia, which may cause deterioration of binocular vision 1
• The rate of conversion from intermittent to constant exotropia is generally low when measured with validated control measures 4

Diagnosis

Diagnosis involves:

• Comprehensive eye examination
• Cover-uncover test or Hirschberg light reflex test
• Prism and alternate cover test or Krimsky test to measure the angle of deviation
• Assessment of binocular sensory status using Worth 4-Dot Testing and stereoacuity tests
• Evaluation of extraocular muscle function
• Cycloplegic refraction to assess refractive errors

Management Considerations

Management options include:

1. Observation: Young children with intermittent exotropia and good fusional control can often be followed without surgery due to low rates of deterioration 1

2. Non-surgical approaches:

   • Correction of refractive errors
   • Alternating occlusion
   • Over-minus lenses
   • Orthoptic exercises/vision therapy
   • Base-in prism 5

3. Surgical intervention: Indicated when there is:

   • Progression to constant or nearly constant deviation
   • Reduced stereopsis
   • Negative effect on social interactions 1

Both unilateral recess-resect procedures and bilateral lateral rectus recessions are effective initial surgical approaches for intermittent exotropia 1.

Important Considerations and Pitfalls

• Pseudoexotropia is not true strabismus but is caused by a disparity between the visual and anatomic axes of the eyes (positive angle kappa) 1
• Exotropia can be associated with other conditions like Duane syndrome, congenital fibrosis syndrome, craniofacial abnormalities, and ocular myasthenia gravis 1
• Careful differentiation between intermittent and constant exotropia is important for management decisions
• Early detection and management are important to prevent deterioration of binocular vision
• Recurrence after surgical correction is common 5