Effectiveness of office based vergence/accommodative therapy for the treatment of intermittent exotropia is investigated through a randomized clinical trial

Purpose of study:

i) To evaluate the short-term effectiveness of office based vergence/accommodative therapy (OBVAT) for improving control of intermittent exotropia compared to observation alone; ii) To evaluate the long-term effectiveness of OBVAT for improving control of intermittent exotropia compared to observation alone; iii) To determine the natural history of intermittent exotropia among patients aged 6 to < 18 years who have baseline near stereoacuity of 400 arc sec or better using the Preschool Randot stereotest

Inclusion Criteria:

1. 6 to <18 years old

2. Distance exodeviation between 10 and 30 prism diopters (PD) measured by prism and alternate cover test (PACT)

3. Near deviation not exceeding the distance deviation by >10PD by PACT (i.e., convergence insufficiency type intermittent exotropia excluded)

4. Control of deviation meeting all the following criteria based on the office control score scale:

   4.1 Intermittent or constant exotropia at distance (mean of 3 baseline assessments of distance control ≥ Grade 2)# 4.2 Intermittent exotropia or exophoria at near (at least 1 of 3 assessments of near control at the baseline visit Grade 0-4) or orthophoria

5. Stereoacuity: near stereoacuity of 400 arcsec or better by the Preschool Randot stereotest

6. Cycloplegic subjective refraction spherical equivalent (SE) refractive error between -6.00 diopters (D)and +3.50 D inclusive in either eye

7. Must be wearing the updated refractive correction (spectacles) for at least 2 weeks if refractive error (based on cycloplegic subjective refraction performed within 6 months) meets any of the following:

   7.1 Myopia >-0.50 D spherical equivalent in either eye 7.2 Anisometropia >1.00 D spherical equivalent 7.3 Astigmatism in either eye >1.50 D

8. Refractive correction must meet the following guidelines:

   8.1 Anisometropia spherical equivalent must be within 0.25 D of the full anisometropic difference 8.2 Astigmatism cylinder must be within 0.25 D of full correction and axis must be within 5 degree 8.3 For hyperopia and myopia, the spherical component can be reduced by investigator discretion provided reduction is symmetrical and results in residual (i.e., uncorrected) spherical equivalent refractive error that does not exceed +3.50 D spherical equivalent hyperopia or -0.50 D spherical equivalent myopia

9. Gestational age >34 weeks

10. Birth weight >1500 g

11. No previous surgical or nonsurgical treatment for intermittent exotropia other than single vision refractive correction (e.g. progressive addition lens, bifocals, patching, or deliberate over-minus with spectacles >0.50 D)

12. No prior office-based vision therapy for any reason

13. No prior strabismus surgery or botulinum injection, intraocular surgery, or refractive surgery

14. No planned strabismus surgery

15. Visual acuity correctable to at least 20/25 or better at distance and near in each eye.

    • Inclusion criteria 4.1 may be changed to "Intermittent or constant exotropia at distance (mean of 3 baseline assessments of distance control ≥ Grade 1" if there is difficulty in patient recruitment.

Exclusion Criteria:

1. Amblyopia, nystagmus, restrictive or paretic strabismus
2. Regular use of any ocular or systemic medications known to affect accommodation or vergence system, such as atropine, pirenzepine, and anti-epileptic medications, in the most recent 3 months
3. Developmental disability, attention-deficit/hyperactivity disorder (ADHD), or learning disability diagnosis in children that in the investigator's discretion would interfere with office-based treatment
4. Relocation anticipated within 2 year
5. Significant ocular or neurologic disorders (e.g. cerebral palsy) other than strabismus
6. Vertical deviation greater than 3 pd
7. Household member already in the study