Convergence insufficiency

Overview
Convergence insufficiency is a sensory and neuromuscular anomaly of the binocular vision system, characterized by an inability to converge the eyes or sustain convergence.

Symptoms
The symptoms and signs associated with convergence insufficiency are related to prolonged, visually-demanding, near-centered tasks. They may include, but are not limited to, diplopia (double vision), asthenopia (eye strain), transient blurred vision, difficulty sustaining near-visual function, abnormal fatigue, headache, and abnormal postural adaptation, among others. Note that some Internet resources confuse convergence and divergence vergence dysfunction, reversing them.

Diagnosis
Diagnosis of convergence insufficiency is made by an eye care professional skilled in binocular vision dysfunctions to rule out any organic disease. Convergence insufficiency characterized by one or more of the following diagnostic findings: High exophoria at near, reduced accommodative convergence/accommodation ratio, receded near-point of convergence, low fusional vergence ranges and/or facility.

Treatment
Convergence insufficiency may be treated with convergence exercises prescribed by an orthoptist or vision therapist. Some cases of convergence insufficency are successfully managed by prescription of eyeglasses with therapeutic Prism (optics) and/or lenses.

In 2005, the Convergence Insufficency Treatment Trial (CITT) published two large, randomized clinical studies. The first demonstrated that in-office based vision therapy was more effective than home based treatment for convergency insufficiency in 9 to 18 year old children. The second found similar results for adults 19 to 30 years of age.

Prevalence
A British survey found that less than 1 in 300 patients receiving optometric eye examinations had convergence insufficiency and a Spanish study found that nearly 1 in 100 (0.8%) of symptomatic patients in an optometric clinic had CI. In contrast, studies conducted by the Southern California College of Optometry found that approximately 1 in 8 (13%) of fifth and six grade children examined during visual screenings had the disorder as did nearly 1 in 5 (17.6%) of 8 to 12 year olds receiving examinations at optometry clinics. A recent Romanian study revealed that roughly 3 in 5 (60.4%) of young adult patients complaining of blurred vision at near work suffered from convergence insufficiency.