Inclusion Criteria 

• Convergence Insufficiency Group
  • 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 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 
  • 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
• Divergence Insufficiency Group
  • Adults ≥18 years of age
  • Adult-onset Divergence insufficiency 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
    • 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 
  • Ability to understand and complete a survey
  • Investigator is initiating treatment with prism, orthoptic exercises, botulinum toxin injection or surgery
  • If 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
• Small-angle Hypertropia Group
  • 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
  • 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
    • Parkinson's disease can be enrolled if of non-paretic deviation
  • No inferior or superior oblique overaction defined as 2+ or greater
  • Ability to fuse with prism in space
  • 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