A potential relationship between convergence insufficiency (CI) and attention deficit hyperactivity disorder (ADHD) has been uncovered by researchers at the Department of Ophthalmology, Ratner Children's Eye Center, University of California, San Diego.

"We report an apparent three-fold greater incidence of ADHD among patients with Convergence Insufficiency when compared with the incidence of ADHD in the general US population (1.8-3.3%). We also note a seeming three-fold greater incidence of CI in the ADHD population. This may simply represent an association and not be a causative relationship. Until further studies are performed, however, patients diagnosed with ADHD should be evaluated to identify the small subset that may have CI -- a condition that responds well to treatment."
Granet D.B., Gomi C.F., Ventura R, Miller-Scholte A. The relationship between convergence insufficiency and ADHD. Strabismus. 2005 Dec;13(4):163-8.

A study by Southern California College of Optometry reported similar findings:
"The results suggest that school-aged children with symptomatic accommodative dysfunction or Convergence Insufficiency have a higher frequency of behaviors related to school performance and attention as measured by the CPRS-R:S."
Borsting E, Rouse M, Chu R. Measuring ADHD behaviors in children with symptomatic accommodative dysfunction or convergence insufficiency: a preliminary study. Optometry. 2005 Oct;76(10):588-92.