Observation Versus Occlusion Therapy for Intermittent Exotropia (IXT2)

Inclusion Criteria:

• Age 12 months to < 11 years

• Intermittent exotropia (manifest deviation) meeting all of the following criteria:

  • Intermittent exotropia at distance OR constant exotropia at distance and either intermittent exotropia or exophoria at near
  • Exodeviation at least 15PD at distance OR near measured by prism and alternate cover test (PACT)
  • Exodeviation at least 10PD at distance measured by PACT
• No previous surgical or non-surgical treatment for IXT (other than refractive correction)
• Visual acuity in the worse eye at least 0.3 logMAR (20/40 on ATS HOTV or 70 letters on E-ETDRS) for children ≥ 3 years of age
• No interocular difference of visual acuity more than 0.2 logMAR (2 lines on ATS HOTV or 10 letters on E-ETDRS) for children ≥ 3 years of age
• No hyperopia greater than +3.50 D spherical equivalent in either eye
• No myopia greater than -6.00 D spherical equivalent in either eye
• No prior strabismus, intraocular, or refractive surgery
• No abnormality of the cornea, lens, or central retina
• Investigator willing to observe the IXT untreated for 3 years unless specific criteria for deterioration are met

Exclusion Criteria:

• Pure phoria at both distance and near
• Prior non-surgical treatment for IXT other than refractive correction (e.g., vergence therapy, occlusion, vision therapy/orthoptics, or deliberate over-minus with spectacles more than 0.50D)
• Previous amblyopia treatment other than refractive correction within 1 year
• Vision therapy/orthoptics for any reason within the last year
• Interocular visual acuity difference more than 0.2 logMAR (2 lines on ATS HOTV for patients 3 to < 7 years old or 10 letters on E-ETDRS for patients ≥ 7 years old) (patients ≥ 3 years only) and/or investigator plans to initiate amblyopia treatment at this time.
• Limitation of ocular rotations due to restrictive or paretic strabismus
• Craniofacial malformations affecting the orbits
• Ocular disorders which would reduce visual acuity (except refractive error)
• Prior strabismus surgery or botulinum injection, intraocular surgery, or refractive surgery
• Strabismus surgery planned
• Known skin reactions to patch or bandage adhesives
• Significant neurological impairment such as cerebral palsy. Patients with mild speech delays or common reading and/or learning disabilities are not excluded.
• Investigator planning to change refractive correction at this time (if the patient is otherwise eligible, the investigator should consider prescribing refractive correction and bringing the patient back at a later time for enrollment)