Base-in Prism Spectacles for Intermittent Exotropia

The objective of this short-term, pilot randomized trial comparing spectacles with relieving prism to spectacles without prism is to determine whether to proceed to a full-scale, longer-term randomized trial. This decision will be based primarily on assessing the initial (8-week) response to prism by comparing treatment groups on the following outcomes:

* Mean distance intermittent exotropia (IXT) control score (the mean of 3 control scores) (primary outcome)
* The proportion of participants demonstrating a "treatment response," defined as ≥1 point improvement in the mean distance IXT control score without spontaneous exotropia during control testing (secondary outcome)
* The proportion of participants reporting adverse effects and good/excellent spectacle wear compliance


Eligibility Criteria:
Inclusion Criteria:

Intermittent Exotropia meeting all of the following criteria:

* Age 3 to 13 years
* Mean distance control score of ≥2.00 points with at least 1 measure of 3, 4, or 5 points (i.e, spontaneous tropia) from the 3 assessments during the exam
* A near control score ≤4 on at least 1 of 3 assessments (cannot have score of 5, 5, 5)
* Distance exodeviation between 16 Prism Diopters (Δ) and 35 Δ (inclusive) by PACT
* Near exodeviation between 10 Δ and 35 Δ (inclusive) by PACT
* Near deviation does not exceed distance deviation by more than 10 Δ by PACT (i.e., convergence insufficiency-type IXT excluded)
* Refractive error between -6.00 Diopters (D) spherical equivalent (SE) and +2.50 D SE (inclusive) (based on a cycloplegic refraction performed within 7 months but prior to the day of enrollment)
* Refractive correction (must be worn for at least 1 week if refractive error meets any of the following (based on a cycloplegic refraction performed within 7 months but prior to the day of enrollment):

  * SE anisometropia ≥1.00 D
  * Astigmatism ≥1.00 D in either eye
  * SE myopia ≥-0.50 D in either eye
* If spectacles have been prescribed and are worn, they must meet the following pre- enrollment criteria:

  * SE anisometropia corrected to within 1.00 D of full SE anisometropic difference
  * Astigmatism corrected to within 1.00 D of full magnitude; axis within 10 degrees if astigmatism ≤1.00 D and axis within 5 degrees if astigmatism \>1.00 D

Exclusion Criteria:

* Dissociated vertical deviation (DVD)
* Vertical deviation \>3 Δ in primary gaze at distance or near
* Patterns (such as an "A" or "V" pattern) with a downgaze measurement of \>10 Δ difference from straight ahead by PACT, measured per investigator's routine method
* Treatment for IXT or amblyopia (other than refractive correction) within the past 4 weeks, including vision therapy, orthoptics, patching, atropine, or other penalization
* Substantial overminus spectacles (spectacles overminused by more than 1.00 D SE than the most recent cycloplegic refraction and also results in minus SE power in the spectacles; underplussing is allowed) within the past 4 weeks
* Prior strabismus, intraocular, or refractive surgery (including BOTOX injection)
* Previous use of prism spectacles

Additional Eligibility Criteria for Randomization Based on Prism Adaptation Testing

* Exodeviation by PACT while wearing "trial" relieving prism for 30 minutes is smaller at distance or near than measured during initial testing (e.g. not fully adapting to prism at both distances)
* No new esotropia on cover test at near while wearing "trial" relieving prism for 30 minutes, compared with enrollment measurement taken without prism
* No esodeviation \>6 Δ on PACT at near while wearing "trial" relieving prism for 30 minutes