Inclusion Criteria:

• Age 3 to < 11 years
• Intermittent exotropia (manifest deviation) meeting all of the following:
  • Intermittent exotropia at distance OR constant exotropia at distance and either intermittent exotropia or exophoria at near
  • Largest exodeviation at either distance, near OR remote distance between 15 and 50 PD (inclusive) by prism and alternate cover test (PACT)
  • Exodeviation at least 15 PD at distance and near by PACT
  • Basic type or pseudo divergence excess type
• Stereoacuity of 400 arcsec or better at near by Preschool Randot stereotest (better of 2 measures)
• Visual acuity in the worse eye at least 0.3 logMAR (20/40 on ATS HOTV or 70 letters on E-ETDRS)
• No interocular difference of visual acuity more than 0.2 logMAR (2 lines on ATS HOTV or 10 letters on E-ETDRS testing)
• Absence of high AC/A ratio (exclude > 6:1)
• No previous intraocular surgery, strabismus surgery, or botulinum toxin treatment
• Investigator planning to perform surgery for correction of IXT
• No hyperopia greater than +3.50 D spherical equivalent (SE) in either eye

Exclusion Criteria:

• Coexisting vertical deviation, oblique muscle dysfunction, DVD, or A or V pattern, any of which the investigator plans to address with vertical transposition of horizontal rectus muscles, oblique surgery, or vertical rectus muscle surgery, i.e., only small vertical deviations, oblique muscle dysfunction, DVD, and A or V patterns not requiring surgery are allowed
• Limitation of ocular rotations due to restrictive or paretic strabismus
• Craniofacial malformations affecting the orbits
• Interocular visual acuity difference of 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) and/or investigator plans to initiate amblyopia treatment at this time.
• High AC/A ratio (exclude > 6:1 by gradient method)
• Prior strabismus surgery or botulinum toxin injection
• Ocular disorders that would reduce visual acuity (except refractive error)
• Prior intraocular or refractive surgery
• Significant neurological impairment such as cerebral palsy. Patients with mild speech and/or learning disabilities are eligible.
• 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).