Binocular vision comes from the process of converging images from each eye into one image.
This lesson reviews a dysfunction of this ability called convergence insufficiency. Definitions, symptoms, and treatments are covered.
In days gone by, before digital cameras, taking pictures was always a bit of a gamble. When the film was processed, it was fun (or not) to see how many pictures came out looking blurring or with double images on them. If you moved while snapping the picture, it could create that double image blur, leaving you with one picture that had ghosts of two images on it. That is how we would see if we didn’t have binocular vision, the process of taking the two images from the eyes and blending them into a single image including depth perception information.
So, what do we do when our eyes are not working together correctly to give us a single merged image from our two eyes? This lesson covers convergence insufficiency, which occurs during close vision work when the eyes do not cooperate with each other to bring a single image to the brain.
Convergence insufficiency is a dysfunction of the eyes that causes them not to track equally, thus not converging (focusing) on a single image. It occurs with close vision scenarios such as reading. The eyes do not focus on the same spot due to a lack of turning inward at the same angle. Because the eyes do not converge on one spot, the focus of the image is off and the result is a lack of binocular vision.Patients are normally diagnosed in childhood due to problems arising in school.
Basically, what happens is that when a person tries to focus on a word to read it, one eye randomly swings away from the image of focus sending alternate visual information to the brain. This lack of convergence (focusing on a single image) denies the brain the opportunity to use its key binocular vision to merge the images from each eye into a single picture to interpret. Without binocular vision, getting meaning from visual stimuli can be difficult and frustrating. The brain has to figure out which image is the intended target and focus effort on interpreting that image and ignoring the image from the eye that is swinging. The double vision effect given by the swinging eye is similar to the double image on old fashion film when the camera moves during exposure. Two images are seen – neither perfectly.
Symptoms for convergence insufficiency are:
- Double vision
- Blurry vision
- Eye strain
- Loss of concentration
- Difficulty reading (e.
g. losing one’s place often)
These symptoms are most likely to come to light at school and may be misinterpreted as a learning disability. This is because most symptoms of convergence insufficiency appear during close vision reading resulting in a scenario that appears to show a child having trouble reading instead of a child having trouble seeing. It is important to have a child’s vision tested at the beginning of any learning intervention to rule out physical hindrances to the learning process.
The good news is that, in most cases, convergence insufficiency can be treated and corrected completely. Once treated, patients can feel relief from symptoms for long stretches of time.
However, it is possible for symptoms to return after periods of sickness or when the eyes are not given proper rest. In the case of treated symptoms returning, normally a repeat of exercise strategies is enough to bring back the full remission of symptoms.Treatment can be categorized by how mild or severe the case is.
Normally, the main issue in convergence insufficiency is a lack of strength in the eye muscles, so exercises can be used to train the muscles in the weaker eye (the wandering eye) to support it in focusing on close vision. Medical professionals prescribe convergence exercises. Depending on the age and geographical location of the patient, sometimes computer programs are used to assist with convergence strength building. These cases are the most common and least severe cases of convergence insufficiency.
In more moderate cases of convergence insufficiency, special glasses or patches might need to be worn. The glasses, called base-out prisms cause the eyes to have to work harder (thus build more muscles).
They can’t be worn long due to the level of fatigue caused, but they are similar to having short intense workouts for the eye muscles.Patches or other vision blocking methods are used only for relief from double vision when a patient has to read or practice close vision for long periods of time. It is not optimal, but in patients that must do a lot of close work, sometimes it is better for them to be able to block the problem temporarily rather than aggravate the symptoms of the problem.
It is very rare to need long term use of base-in prism glasses (tool used to converge the eyes artificially), but some patients do not improve even with strengthening therapies and must adopt life-long assistance techniques.
A final option for those that do not respond to any other therapies is surgery. Surgery is designed to adjust the muscles in the eyes so that they track perfectly with each other.
Convergence insufficiency is a lack of binocular vision at close range due to the eyes not focusing on a single spot. Symptoms include difficulty reading, double vision, lack of attention and eye strain. Treatment is normally in the form of convergence exercises, but in severe cases it can require surgery.