|Convergence insufficiency (CI) is a common eye muscle coordination problem. When reading or doing close work, a person's eyes must turn in (converge) for the words to be clear and single. This usually happens easily, without thinking. In CI, the eyes do not turn in easily and as a result, extra convergence effort must be used to force the eyes to turn in. This additional effort can cause a number of symptoms such as eyestrain, headaches, blurred vision, double vision, difficulty concentrating, loss of place and concentration, and reading slowly. CI has no obvious signs and is only detected through an eye examination.
Virtually all people that have convergence insufficiency have 20/20 vision. However, it is not enough to have 20/20 vision and be able to see clearly. For the visual system to function properly we must use our two eyes together in a very precise and coordinated fashion. This ability is referred to as eye teaming or eye coordination. The technical term for this ability is BINOCULAR VISION.
Every time we look at something we must accurately aim the two eyes directly at the object of interest. Each eye sends an image to the part of the brain that is involved in the process of seeing. This part of the brain, called the visual cortex, then attempts to combine these two images to make form one "fused" image. If these images are identical the result is normal, clear, single vision and a perception of depth. If, however, the two eyes are not performing in a coordinated manner the visual cortex will receive two different images and will experience double vision.
There are many types of eye teaming or binocular vision problems. The eyes may tend to drift in, out, up, down, or a combination of these variations. The most common eye teaming problem is convergence insufficiency in which the eyes tend to drift outward when reading or when engaged in any near distance visual activity.