Evaluation of Exotropia After Patching the Eye or After Prism Adaptation

• Patching (Procedure): The subject will occlude the non-dominant eye for 24 hours.
• Prism Adaptation (Procedure): The subject will undergo prism adaptation targeting the pre-occlusion distance angle for 1-2 weeks. • Fresnel prism(s) will be applied to the patient's spectacles equaling the distance angle between the two eyes. At the examiner's discretion depending on the size of the deviation, the prism(s) can be placed solely over the non-dominant eye, or split between the 2 eyes in some combination which results in equalization of the distance exotropia. If the distance angle calls for an amount of prism that cannot be exactly replicated with Fresnel prisms (e.g., 32 PD), the amount of prism used will be determined by rounding down to the nearest practical amount at examiner discretion.

Primary outcomes

• Percent of participants reclassified as divergence excess exotropia [2 weeks]: Percentage of patients with distance and near exotropia measurements within 2.5 prism diopters on alternate prism and cover testing after 24 hours of patching or 7-14 days of fresnel prism use.
• Percent of participants reclassified as simulated divergence excess exotropia [2 weeks]: Percentage of patients with distance and near exotropia measurements differing by more than 2.5 prism diopters on alternate prism and cover testing after 24 hours of patching or 7-14 days of fresnel prism use.

Sex: All, ages: any to 17 Years

Inclusion Criteria:

* Diagnosed with divergence excess exotropia according to standard criteria (see Study Procedures for specifics)
* No prior strabismus surgery
* Able to cooperate with testing (by examiner determination)
* Neurologically normal except for strabismus (ADHD and autism spectrum are not exclusion criteria as long as the subject can cooperate for necessary testing)
* Not amblyopic at the time of enrollment (best-corrected visual acuity in both eyes of 20/40 or better)
* Under 18 years of age. There is no lower age limit as long as the subject can cooperate for the required testing.
* No diagnosis of dissociated vertical deviation

Exclusion Criteria:

* No diagnosis of divergence excess exotropia according to standard criteria (see Study Procedures for specifics)
* Prior strabismus surgery
* Unable to cooperate with testing (by examiner determination)
* Diagnosed with a neurological disorder (ADHD and autism spectrum are not exclusion criteria as long as the subject can cooperate for necessary testing)
* Best-corrected visual acuity in either eye worse than 20/40
* 18 years of age or older
* Diagnosed with dissociated vertical deviation