Convergence insufficiency

Convergence insufficiency (CI) is a common, yet not frequently diagnosed eye coordination problem in which the eyes drift outward when reading or doing close work.
Child has difficulty reading

Causes & risk factors

Convergence insufficiency (CI) is caused by a simple “lack of proper communication” between the nerves and the muscles that control eye movements. The muscles surrounding the eye (there are six) are plenty strong, but the nerves that control these muscles are not sending the proper message to turn inward enough to aim at the target (page or screen).


There are many symptoms listed below. An easy way to explain how it really feels is by comparing your eyes when reading to driving along the interstate. When driving is normal, your car is usually in one lane but there are two lanes that can be used, thus giving a feeling of comfort. When you enter a construction zone, squeezed down to one lane with concrete barriers on each side of you, there is still plenty of room for your car, but not as much as with two lanes. The result is you most likely will slow down, hold the wheel tighter, stiffen your shoulders, and overall feel more stressed.

Your eyes have a similar comfort zone called the fusional range. Your fusional range is how far inward and how far outward your eyes can move and still see single and comfortable. If that range is narrow, just like the construction zone, you will slow down and feel more stressed when you are reading because there is one thing your brain hates and that is seeing double. In order to not see double, eyes start working very hard to maintain single vision.

This can lead to a multitude of symptoms including eyestrain (especially with or after reading), plus:

  • Headaches.
  • Blurred vision.
  • Double vision.
  • Inability to concentrate.
  • Short attention span.
  • Frequent loss of place.
  • Squinting, rubbing, closing, or covering an eye.
  • Sleepiness during the activity.
  • Trouble remembering what was read.
  • Words appear to move, jump, swim, or float.
  • Problems with motion sickness and/or vertigo.


CI can almost be diagnosed by listening to the patient describe their symptoms. If these symptoms (all or some) are noted, extra testing can be performed to diagnose or rule out CI. It is important to note that most routine eye exams will not include specific testing for CI, so it is important that the patient or parent explains in detail the symptoms he/she is having. That will signal the doctor to add extra testing to see how well the eyes work together.


Treatment can be active or passive. Active treatment involves fairly intense eye exercises that retrain the nerves to aim the eyes properly and increase the fusional range. The most successful treatment involves home plus office therapy. The least successful involves an older form of treatment called “pencil push-ups". Pencil push-ups can help but only when incorporated into a complete therapy program. Active treatment can last up to 90 days or more and typically the results are permanent. Passive treatment is more like a crutch that works only when in place. Prisms can be incorporated into reading glasses that redirect light entering the eyes. Think of it as the lenses doing the work the nerves don’t know how to do.


In the case of CI, treatment is part of the prevention. This is because if the condition is not properly treated, it can progress into a much more serious condition called intermittent exotropia. This is the brain's answer to coping with double vision and the stress of eyes not working as a team. The eyes may drift further apart and simply begin working independently rather than as a team. This can lead to a whole host of new problems. Our brain is wired for two eyes to work together and when this doesn’t happen, the problems begin to go beyond discomfort while reading. The use of one eye is suppressed.

Suppression of vision in one eye causes loss of binocular (two-eyed) vision and depth perception. Poor binocular vision can have a negative impact on many areas of life, such as coordination, sports, the judgment of distances, eye contact, motion sickness, etc. Consequently, a person with convergence insufficiency who is suppressing one eye can show some or all of the following symptoms:

  • Trouble catching balls and other objects thrown through the air.
  • Avoidance of tasks that require depth perception (games involving smaller balls traveling through the air, handicrafts, and/or hand-eye coordination, etc.)
  • Frequent mishaps due to misjudgment of physical distances (particularly within twenty feet of the person's body), such as:
    • Trips and stumbles on uneven surfaces, stairs, and curbs, etc.
    • Frequent spilling or knocking over objects.
    • Bumping into doors, furniture, and other stationary objects.
    • Sports and/or car parking accidents.
  • Avoidance of eye contact.
  • Poor posture while doing activities requiring near vision.
  • One shoulder is noticeably higher.
  • Frequent head tilt.
  • Problems with motion sickness and/or vertigo.

In summary, CI is a common but frequently missed diagnosis (one can have uncorrected vision in each eye of 20/20 vision and still have CI so screenings at work and school will totally miss it). CI is also very treatable if diagnosed. However, treatment is patient intensive. If the patient doesn’t do the therapy, there will be no improvement.

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