"Convergence insufficiency" is the visual condition or disorder in which a person has difficulty comfortably and efficiently converging the two eyes together (moving the eyes inward and outward for focusing, attention, and comprehension). Convergence Insufficiency problems hurt reading, playing, and working at near and far distances for anything more than very short periods of time.
"Convergence" is the act of aiming and coordinating the two eyes at nearer distances or "reading distance." For example, if a person crosses his eyes to look at his nose, his eyes are fully "converged." To read, a person has to partially "converge" the two eyes on the reading material and the convergence of the eyes needs to be sustains effortlessly during the reading period for good comprehension and learning.
In many cases of convergence insufficiency, the eyes "look" normal, but the effort that the person has to put out to see within arm's reach or "reading distance" is so great that it causes discomfort, headaches, drowsiness, eyestrain, lack of comprehension or lapses in concentration or attention during reading and computer work. To learn more about this type of problem see "Eye-Muscle Coordination" on the "7 Visual Abilities" web page. Also see "Reading Problems and Dyslexia" on the "Vision and Learning" web page. In addition, convergence insufficiency can also cause almost any of the symptoms listed in the "Adult Self Assessment" and "Children's Screening" web pages.
To learn more, see Convergence Insufficiency Treatment and Therapy
and Reading Disability
"In my opinion, the prospective study was well planned and is essentially double blinded. . . The results support the proposition that application of orthoptics [a form of vision therapy] to all learning/reading disabled or deficient children who manifest convergence insufficiency should be the first line of therapy . . ."
See the "Scientific Support" web page for an exact reference.