A Prospective Observational Study of Adult Strabismus

Eligibility Criteria for Convergence Insufficiency (CI) Group: The following inclusion criteria must be met for the subject to be enrolled into the study: * Adults ≥18 years of age (adult onset of CI not required) * No strabismus surgery within the past 10 years * CI Symptom Survey score ≥21 points * Near exodeviation of ≥4∆ and at least 4∆ larger than at distance by PACT * Distance exodeviation ≤15∆ by PACT * Vertical deviation ≤2∆ at distance and near by PACT * No constant exotropia at distance or near * Reduced positive fusional vergence (PFV) at near (\<20∆ or fails Sheard's criterion that the PFV measures less than twice the magnitude of the near phoria) * Near point of convergence (NPC) of ≥6 cm break * Visual acuity 20/50 or better in both eyes by ETDRS or Snellen * No paralytic strabismus (e.g., 3rd, 4th, or 6th cranial nerve palsies, skew deviation, Duane syndrome) * No restrictive strabismus (e.g., blowout fracture, thyroid eye disease, post scleral buckle, Brown syndrome) * No monocular diplopia * No paretic strabismus, thyroid eye disease, myasthenia gravis, chronic progressive external ophthalmoplegia, or eye movement abnormalities associated with known neurological disease. Patients with Parkinson's disease can be enrolled if non-paretic deviation. * No inferior or superior oblique overaction defined as 2+ or greater * Ability to fuse with prism in space (see section 2.4.1) * Ability to understand and complete a survey * Investigator is initiating treatment wi…