Neural Mechanism of Vision Therapy for Patients With Convergence Insufficiency
Condition: Convergence Insufficiency
MeSH terms: Ocular Motility Disorders
Study type: Interventional

Summary: 
      Convergence insufficiency (CI) is a prevalent binocular vision disorder with symptoms that
      include double/blurred vision, eyestrain, and headaches when engaged in reading or other near
      work. CI is present in 4% of the population where approximately 27% of CI patients do not
      improve even with validated therapy. The project will quantitatively study changes in
      convergence eye movements and neural substrates before and after validated therapy in CI
      patients. This knowledge can lead to improvements in currently validated therapy, reduction
      in therapy sessions, and reduced healthcare costs.
    

Detailed description: 
      Convergence insufficiency (CI), a prevalent binocular vision disorder in adults and children,
      is characterized by greater exophoria at near than at distance, reduced fusional convergence
      amplitude, receded near point of convergence, and a reduced accommodative convergence over
      accommodation ratio (AC/A). CI is associated with symptoms that include double/blurred
      vision, eyestrain, and headaches when engaged in reading or other near work, thus interfering
      with activities of daily living. The recent NEI/NIH multi-center randomized clinical trial,
      the Convergence Insufficiency Treatment Trial (CITT), demonstrated the effectiveness of
      Office-Based Vergence and Accommodative Therapy with home reinforcement (OBVAT) for CI,
      reporting 73% of patients have sustained improvements of vision function and symptoms. The
      team published the first fMRI neural substrate data evoked using convergence eye movements in
      CI patients before and then post-OBVAT. The team's results suggest that with the reduction of
      visual symptoms, the following were observed: 1) an increase in the percent signal change of
      functional activity in the frontal eye fields, posterior parietal cortex and the cerebellar
      vermis, 2) an increase in convergence peak velocity, 3) a decrease in the near point of
      convergence, 4) an increase in positive fusional amplitude and 5) a reduction in the amount
      of exophoria at near. The aims of the current proposal are to test the following two
      hypotheses as potential underlying mechanisms of CI that may be improved post OBVAT: 1) a
      reduced ability to adapt vergence in near and far space via the 'slow' component of vergence
      and 2) a reduced ability to quickly diminish disparity error via the 'fast' component of
      vergence. Not only will our quantitative methods integrated with established CITT standards
      address important questions about potential mechanisms causing CI, this proposal seeks to
      identify how a validated vergence therapy may remediate symptoms. This proposal will
      determine whether either of these two potential mechanisms are causing CI by quantifying the
      following: 1) rate and magnitude of phoria adaptation, 2) forced vergence fixation disparity
      curves, 3) peak velocity of convergence eye movements (studying visual cues such as
      disparity, accommodation and proximal stimuli in isolation and combination), and 4) the
      functional activity of the fast and slow vergence neural substrates prior to, and then after,
      OBVAT. The assembled study team is particularly knowledgeable in terms of OBVAT, convergence
      insufficiency, optometry, vision science, oculomotor research, functional imaging, modeling
      and statistics with the necessary resources to successfully complete both aims of this study.
      Results from the project's aims can lead to targeted treatments with improved success rates,
      potentially reducing the time to remediate symptoms, and ultimately reducing health care
      costs.
    

Intervention name(s): Office Based Vergence and Accommodative Therapy
Intervention type(s): Behavioral
Intervention description(s): Exercises that will stimulate disparity vergence or accommodation independently and then combined will be used.
Allocation: Randomized
Intervention model: Parallel Assignment
Masking: Quadruple (Participant, Care Provider, Investigator, Outcomes Assessor)
Primary purpose: Treatment