Convergence insufficiency (CI) is a condition in which a person's eyes tend to drift outward when looking at objects at close distances, and their ability to converge (turn the eyes towards each other) is insufficient . People with CI can develop symptoms when they try to perform near-based activities, such as reading, working on a computer or smartphone, watching video, or playing video games. Symptoms include performance-related problems (loss of concentration, loss of place in reading, slow reading) and eye-related symptoms (eye pain, diplopia, blurred vision, headache). CI is not a condition caused by muscle weakness. Instead, in CI, the neuromuscular ability (the nerve control of muscle function) to compensate for the poor convergence is abnormal.

To see objects as clear, separate images, our brains merge information from both eyes. The process requires the eyes to come together and focus on the same point. As objects get closer to the face, the eyes must turn inward to maintain convergence and eye alignment. Most people can converge up to an inch from the nose. But people with CI may have trouble converging and maintaining eye alignment when looking at objects close by. People with CI often experience blurred or double vision, eye strain, and discomfort reading or doing activities near work for a long period of time.

CI is a common eye condition in both children and adults. If there is no concussion or other brain injury, we don't know why some people develop CI, but we do know that between 4 and 17 percent of children and adults have a CI. Although CI usually starts in childhood, it can start at any age, and without treatment, CI can last for many years. Recent studies have shown that CI is very common after concussions that do not go away within a few weeks.

CI is called an eye teaming problem (the ability of the eyes to work together) and is usually not related to refractive errors such as nearsightedness (myopia), hyperopia, or presbyopia (general or age-related farsightedness). There are many other types of eye teaming problems, but CI is the most common. People with 20/20 vision can have CI.

An optometrist or ophthalmologist can diagnose CI by asking questions and examining the patient. The doctor may ask about symptoms such as blurred vision, headache, double vision, and eye strain when focusing close-up for a long time. To diagnose CI, a doctor must take the following measurements:

• Near point of convergence : The point closest to the face where the eyes continue to converge. People with CI usually have a point of convergence in the vicinity, more than 6 cm from the face.
• Positive Fusion Vention : Positive fusion frequency refers to the neuromuscular ability of the eyes to converge inward. This is the main underlying problem related to CI. The physician uses a series of prisms of increasing size and asks de patient to maintain a single view while looking through these prisms.
• Exodeviation : This refers to the tendency of the eyes to drift out and is an important part of the examination. People with CI will have a greater exodeviation when looking at objects close by than when looking at objects far away.
• Accommodation : Accommodation refers to the ability to change focus from far to near. A high percentage of people with CI also have difficulty focusing their eyes on nearby objects.

CI is treated with vision therapy. The goal of vision therapy is to normalize the neuromuscular ability to converge (positive fusion rate). Vision therapy generally involves practicing convergence and focusing on objects with both eyes at different distances. Special equipment is used to stimulate and monitor the alignment of the eyes.

The NEI Convergence Insufficiency Treatment Trial (CITT) has shown that the most effective treatment for CI therapy is in the office, supervised by a trained therapist, with additional exercises at home. Most of the children who received in-office therapy showed normal vision or significant improvement in symptoms after 12 weeks.

The NEI CITT Attention and Reading Trial (CITT-ART) has shown that for children with reading difficulties, CI treatment alone is not sufficient to improve reading performance.