SECONDARY ESOTROPIA OR SECONDARY EXOTROPIA

Question 1

What can cause secondary strabismus?

Answer 1

• Follows loss or impairment of vision
  O Sufficiently severe to completely disrupt fusion – usually loss of foveal function
• Also known as sensory strabismus
• Functional amblyopia may be superimposed on the pathological reason for reduced vision – can be improved with treatment

Question 1

What direction does strabismus tend to occur in secondary deviations at different ages?

Answer 1

• Birth – Exotropia develops: Havertape et al. (2001) congenital vision loss 67% ET and 33% XT
• Early childhood – Esotropia develops
  O Berk et al. (2000) 31 patients presented over 1 year period. Mean age of onset in ET was 22.3 months and in XT 62.1 months. Significantly lower age of onset in ET patients Eighteen patients (58%) had esotropia and 13 (42%) had exotropia.
• Older children / adults – Exotropia develops

Question 2

Investigation of secondary strabismus?

Answer 2

• Determine cause if unknown (particularly babies) - Careful case history
• Modification of investigation depending on VA
• Appropriate target – may need to use light
  -If unable to fix – measurement by Hirschberg’s; Krimsky; prism reflections; CR on synoptophore

Question 2

What does management depends on in secondary strabismus?

Answer 2

O Post-operative diplopia
O Level of VA
O Age of onset (Investigation of possible BSV - need to have developed BSV)

Question 3

What is non-surgical management for secondary strabismus?

Answer 3

• Refractive correction
• Ensure underlying cause treated if possible
• Treat any associated functional amblyopia
• Botulinum Toxin – useful in smaller angles and as a diagnostic tool
  O Woodruff et al. (1999) BT restored BSV in 7% of cases after improved VA in CL wear in unilateral aphakia.
  O Gardner et al. (2008) time interval between injections increase in most patients and angle reduced with long-term BT management (25+ injections)

Question 4

What is surgical management for secondary strabismus?

Answer 4

• Operate on the deviating eye
  O May need supermaximal surgery (even if restriction caused - no BSV potential)
• Esotropia – aim to undercorrect
• Exotropia – aim to overcorrect (unless BSV potential – undercorrect 5Δ)
• Age of patient considered – wait until stable angle

Question 5

What is prognosis in surgery for secondary strabismus?

Answer 5

• Busek-Schneider & Boss (2010) good alignment following surgery for sensory ET & XT
• Turan et al. (2015) better VA potential predictor for higher long-term success post surgery. Better long-term success rate found in secondary ET than XT.
• Multiple past surgeries – may find BT only option (repeated)
• Cosmetically unsightly eye – painted contact lens may be considered