Eligibility and exclusion criteria
| Eligibility criteria: |
| • Age 9 to <18 years. |
| • Best corrected visual acuity of 20/25 or better in both eyes at distance and near. |
| • Willingness to wear eyeglasses to correct refractive error, if necessary. |
| • Exophoria at near at least 4 Δ greater than at far. |
| • Insufficient positive fusional convergence at near (fails Sheard’s criterion). |
| • Receded near point of convergence of ⩾6 cm break. |
| • Appreciation of at least 500 seconds of arc on the forms part of the Randot Stereotest. |
| • CI Symptom Survey-V15 score ⩾16. |
| • Informed consent and willingness to participate in the study and be randomised. |
| Exclusion criteria |
| • CI previously treated with prism, pencil push ups, or office based vision therapy/orthoptics (no more than 2 months of treatment within the past year). |
| • Amblyopia. |
| • Constant strabismus. |
| • History of strabismus surgery. |
| • Anisometropia >1.50 D (spherical equivalent) difference between eyes. |
| • Previous refractive surgery. |
| • Vertical heterophoria greater than 1 Δ. |
| • Systemic diseases known to affect accommodation, vergence, and ocular motility such as multiple sclerosis, Grave’s thyroid disease, myasthenia gravis, diabetes, and Parkinson’s disease. |
| • Any ocular or systemic medication known to affect accommodation or vergence. |
| • Monocular accommodative amplitude less than 4 D in either eye as measured by the push up method. |
| • Manifest or latent nystagmus. |
| • Attention deficit hyperactivity disorder or learning disability diagnosis by parental report that, in the investigator’s opinion, would interfere with treatment. |