What is Convergence Insufficiency?
The textbook definition for Convergence Insufficiency is:
“A neuromuscular abnormality of the binocular system characterised by an inability to converge the two eyes or to sustain the two eyes converged.”
or more simply… this means that the individual has difficulty keeping both eyes turned in and pointing at the same thing when they are doing near work.
This is not eyesight or muscle problem but rather an adaption to the stress of keeping the two eyes turned in (converged) for long periods. The brain chooses to let one eye drift out and suppresses the image from the that eye (so no double vision) and hence alleviates stress of keeping both eyes turned in.
Testing for Convergence Insufficiency
The diagnosis of with Convergence insufficiency is based on 4 main clinical criteria:
- When the eyes drift out (Exophoria) more at near than in the distance.
- > 4 prism Dioptres.
- Receded Near Point of Convergence.
- Can’t turn both eye in to fixate something inside 6 cm form their nose.
- Reduced ranges of maintain single clear near vision.
- Called near Base out Fusional Ranges.
- < 15 prism base out cause loss of fusion.
The reason for the development of a Convergence problem are not fully understood. There are two theories that have been suggested but not scientifically proven as yet:
- Poor convergence development : Due to genetics or poor natural development and with the commencement of school and having to do more prolonged near work (like learning to read) this problem then becomes apparent.
- The volume of prolonged near work has out stripped the stamina to cope with it. This can also happen in the adult eye, especially if you are doing a lot of stressful near centred task (eg new job involving more close work, study, prolonged computer work, fine sewing etc).
The symptoms associated with Convergence insufficiency are usually related to the task that produces the stress, i.e. prolonged near centred tasks. The symptoms may include, but are not limited to the following:
- Visual Stress Symptoms. (Red eyes, sore eyes, transient blurry vision and/or headaches.
- Difficulty sustaining near visual attention. (may actually avoid near task)
- Abnormal posture adaptations such as pulling books closer.
- Occasionally double vision or the letters moving or running.
Double blind studies done in 2008 showed that:
- Visual Therapy intervention was the most successful treatment (72%).
- Doing Pencil Push Ups was successful in 43% of cases.
- Computer Convergence Training was successful in 33% of cases.
We use the following treatment strategy:
- Training Spectacle lenses for all close work.
- These are a little like braces on crooked teeth that gradually straighten the teeth and are then are removed.
- The training lenses help alleviate or reduce the visual point stress and allow the individual to develop better convergence stamina.
- The more they are worn for near work the sooner better convergence abilities are developed, the sooner the spectacles are no longer needed.
- Eye Exercises. (Visual Therapy)
- Visual Therapy on its own is slow to improve stamina problems for the simple reason that for every half hour of therapy might be done at night time; the child/adult has usually been doing 5 or 6 hours of “Anti-therapy” during the day (i.e. demanding close work causing near point stress and the eyes drift apart.)
Duration of Treatment
Generally the training lenses are needed to be worn for all close work including computer work, reading, classroom work etc. They are not for outdoors, TV or for constant wear.
The Golden Rule: If you can touch it with your hands you should have your training spectacles on to see it.
- Most need the training spectacles for 12 – 18 mths before we can reduce or eliminate the need to wear them anymore.
- We will do a 6 week review to ensure the training lenses are developing better convergence abilities.
- If there is little or no change after this time Visual Therapy will also be considered.
- This is only needed in about 40% of cases.
- Visual Therapy requires between 4 to 6 in-office visits (2-3 weeks apart) along with home based activities been done between visits.
- NB: These are generalised guidelines and each case may need to be evaluated on the individual basis. Treatment duration will depend on the particular patient’s condition.