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 with prism, orthoptic exercises, botulinum toxin injection or surgery * If initiating treatment with botulinum toxin or surgery, planned injection or surgery to be within 60 days of enrollment * Single treatment modality is planned (e.g., no combined prism and orthoptic exercises) * Treatment to be initiated has not been used within the past one year Eligibility Criteria for Divergence Insufficiency (DI) Group: The following inclusion criteria must be met for the subject to be enrolled into the study: * Adults ≥18 years of age * Adult-onset DI (at ≥18 years of age) * No prior strabismus surgery * Symptoms of diplopia at distance with a frequency of sometimes or worse in primary position (in current glasses if wearing glasses) * Distance esodeviation of 2∆ to 30∆ and at least 50% larger than at near by PACT * No more than 5∆ difference between right and left gaze by PACT * No more than 10∆ difference between the primary position at distance and either upgaze or downgaze ≤10∆ by PACT * Any coexisting vertical deviation must be less than distance esodeviation and ≤10∆ by PACT * 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 2.4.2) * Ability to understand and complete a survey * Investigator is initiating treatment with prism, orthoptic exercises, botulinum toxin injection or surgery * If initiating treatment with botulinum toxin or surgery, planned injection or surgery to be within 60 days of enrollment * Single treatment modality planned (e.g., no combined prism and orthoptic exercises) * Treatment to be initiated has not been used within the past one year Eligibility Criteria for Small-angle Hypertropia (HT) Group: The following inclusion criteria must be met for the subject to be enrolled into the study: * Adults ≥18 years of age * Adult-onset HT (at ≥18 years of age) * No prior strabismus surgery * Symptoms of diplopia at distance or near with a frequency of sometimes or worse in primary or reading position (in current glasses if wearing glasses) * Vertical deviation ≥1∆ to ≤10∆ at distance and near by PACT * No more than 4∆ difference from the primary in any gaze position by PACT * Any coexisting esodeviation must be less than the vertical deviation * Any coexisting exodeviation ≤10∆ by PACT * No convergence insufficiency as defined in section 2.2.1 * 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 2.4.3) * Ability to understand and complete a survey * Investigator is initiating treatment with prism, orthoptic exercises, botulinum toxin injection or surgery * If initiating treatment with botulinum toxin or surgery, planned injection or surgery to be within 60 days of enrollment * Single treatment modality planned (e.g., no combined prism and orthoptic exercises) * Treatment to be initiated has not been used within the past one year Exclusion Criteria for Convergence Insufficiency (CI) Group: The following criteria exclude a subject from enrollment into the study: * 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 * Constant exotropia at distance or near * Near point of convergence (NPC) of ≤6 cm break * Visual acuity worse than 20/50 either eye by ETDRS or Snellen * Paralytic strabismus (e.g., 3rd, 4th, or 6th cranial nerve palsies, skew deviation, Duane syndrome) * Restrictive strabismus (e.g., blowout fracture, thyroid eye disease, post scleral buckle, Brown syndrome) * Monocular diplopia * 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. * Inferior or superior oblique overaction defined as 2+ or greater * Inability to fuse with prism in space (see section 2.4.1) * Inability to understand and complete a survey * Treatment to be initiated has already been used within the past one year Exclusion Criteria for Divergence Insufficiency (DI) Group: The following criteria exclude a subject from enrollment into the study: * No adult-onset DI (at ≥18 years of age) * Prior strabismus surgery * Distance esodeviation outside the range of 2∆ to 30∆ and less than 50% larger than at near by PACT * More than 5∆ difference between right and left gaze by PACT * More than 10∆ difference between the primary position at distance * Any coexisting vertical deviation more than distance esodeviation and ≥10∆ by PACT * Visual acuity worse than 20/50 in either eye by ETDRS or Snellen * Paralytic strabismus (e.g., 3rd, 4th, or 6th cranial nerve palsies, skew deviation, Duane syndrome) * Restrictive strabismus (e.g., blowout fracture, thyroid eye disease, post scleral buckle, Brown syndrome) * Monocular diplopia * Paretic strabismus, thyroid eye disease, myasthenia gravis, chronic progressive external ophthalmoplegia, or eye movement abnormalities associated with known neurological disease. * Inferior or superior oblique overaction defined as 2+ or greater * Inability to fuse with prism in space (see section 2.4.2) * Inability to understand and complete a survey * Treatment to be initiated has already been used within the past one year Exclusion Criteria for Small-angle Hypertropia (HT) Group: The following criteria exclude a subject from enrollment into the study: * No adult-onset HT (at ≥18 years of age) * Prior strabismus surgery * Vertical deviation ≤1∆ or ≥10∆ at distance and near by PACT * More than 4∆ difference from the primary in any gaze position by PACT * Coexisting esodeviation must not be less than the vertical deviation * Coexisting exodeviation ≥10∆ by PACT * Convergence insufficiency as defined in section 2.2.1 * Visual acuity worse than 20/50 in either eye by ETDRS or Snellen * Paralytic strabismus (e.g., 3rd, 4th, or 6th cranial nerve palsies, skew deviation, Duane syndrome) * Restrictive strabismus (e.g., blowout fracture, thyroid eye disease, post scleral buckle, Brown syndrome) * Monocular diplopia * Paretic strabismus, thyroid eye disease, myasthenia gravis, chronic progressive external ophthalmoplegia, or eye movement abnormalities associated with known neurological disease. * Inferior or superior oblique overaction defined as 2+ or greater * Inability to fuse with prism in space (see section 2.4.3) * Inability to understand and complete a survey * Treatment to be initiated has already been used within the past one year