Convergence insufficiency (CI) is a condition in which a person’s eyes have a tendency to drift outward when looking at objects at near distances, and their ability to converge (rotate the eyes towards each other) is inadequate. People with CI may have symptoms when trying to perform near-based activities such as reading, working on a computer or smart phone, watching video, or playing video games. Symptoms include performance-related problems (loss of concentration, loss of place with reading, reading slowly) and eye-related symptoms (eyes hurt, diplopia, blurred vision, headaches). CI is not a condition caused by a muscle weakness. Instead, in CI the neuromuscular ability (the nerves’ control of muscle function) to compensate for the poor convergence is abnormal.
Why do people with CI have difficulty focusing on near objects?
To see objects as clear, single images, our brains merge information from both eyes. The process requires that the eyes converge and focus on the same point. As objects move closer to the face, the eyes must turn inward to maintain convergence and eye alignment. Most people can converge on objects as close as 2.5 centimeters (1 inch) from the nose. But people with CI can have trouble converging and maintaining eye alignment when looking at near objects. People with CI often experience blurry or double vision, eye strain, and discomfort when reading or doing near work activities over a long period of time.
Who can get CI?
CI is a common eye condition in both children and adults. In the absence of a concussion or other brain injury, we do not know why some people develop CI, but we do know that between 4 and 17 percent of children and adults are thought to have CI. While CI usually begins in childhood, it can begin at any age, and without treatment CI can persist for many years. Recent studies have found that CI is very common after concussions that do not resolve in a few weeks.
How is CI diagnosed?
An optometrist or ophthalmologist can diagnose CI by asking questions and examining the patient. The doctor may ask about symptoms such as blurry vision, headache, double vision, and eye fatigue when focusing near for long periods of time. To diagnose CI, a doctor must take the following measurements:
- Near point of convergence: the closest point to the face at which the eyes continue to converge together. People with CI typically have a near point of convergence more than 6 cm from the face.
- Positive fusional vergence: Positive fusional vergence refers to the neuromuscular ability of the eyes to converge inward. This is the key underlying problem associated with CI. The doctor uses a series of prisms with increasing magnitude and ask the patient to maintain single vision while looking though these prisms.
- Exodeviation: This refers to the tendency for the eyes to drift outward and is a key part of the examination. People with CI will have greater exodeviation while looking at near objects than while looking at far objects.
- Accommodation: Accommodation refers to the ability to change focus from far to near. A high percentage of people with CI also have trouble focusing the eyes on near objects.
How is CI treated?
CI is treated with vision therapy. The objective of vision therapy is to normalize the neuromuscular ability to converge (positive fusional vergence). Vision therapy generally includes practice converging and focusing on objects with both eyes at various distances. Special equipment is used to stimulate and monitor the alignment of the eyes.
Trials have shown that the most effective treatment for CI is in-office therapy, overseen by a trained therapist, with additional at-home exercises. Most children given in-office therapy showed normal vision or significant improvement in symptoms after 12 weeks.