Our eyes are designed to work as a team, but each eye functions independently. When we view an object, the brain receives the image from each eye separately. These images are transmitted via the optic nerves. The brain then combines them into a single picture. In an optimally functioning visual system, the eyes aim to the exact same point in space so that the brain can fuse the 2 images and allow clear comfortable vision. If the eyes aren’t aiming together properly, then the images being recorded are slightly different. This causes confusion in the brain and blurred or double vision.
Unfortunately, about ten percent of school-aged children have eye teaming problems – technically, called convergence insufficiency or convergence excess. At the close up distances required for reading, children with eye teaming problems are only able to aim their eyes together correctly for short periods of time. As their ability to accurately aim their eyes breaks down, their eyes end up pointing at slightly different places on the page.
Children with eye teaming difficulties become tired easily, are distractible, lose place with reading, get headaches and eyestrain and often find school “boring” or too difficult. Some children will end up turning off or “suppressing” one eye to achieve more comfortable vision. Although more comfortable, this is not optimum and such children will become tired and robs the child of concentration.
It is important that children are as visually available for learning as possible. A child does not realise that the way he or she sees is not “normal”.
Glasses and vision therapy can successfully treat both convergence excess and convergence insufficiency.
Convergence Insufficiency (CI) is an eye teaming problem for near visual tasks such as reading or computer work. It is characterized by the eyes inability to converge (or point both eyes toward the near task) and maintain a clear, single image. It manifests as headaches, eye fatigue, poor concentration and print that moves, looks shadowed or is double.
CI can be found in both children and adults and can be the cause of children being diagnosed with ADD or ADHD. Convergence insufficiency will not go away on its own. Instead, the individual learns avoidance, or compensating behaviours such as covering an eye. The most effective and consistent treatment is office based vision therapy to train the eye teaming. This was demonstrated by a 2008 National Eye Institute Study which compared various treatment approaches. The effectivity has also been documented in a newer study by the Mayo Clinic.
Our patients have experienced dramatic changes in work performance, and school performance following therapy for convergence insufficiency.
Imagine how difficult and tiring it would be if words on a page looked something like this:
Convergence Excess means the individual, when they look to near vision tasks, has a natural tendency to aim the eyes closer in than the position they are trying to aim at.
For example someone reading would ideally aim and focus the eyes together on the words on the page, in cases of convergence excess there is usually the situation where the eyes meet to aim at a point closer in than the page.
Often individuals can be noted to work closer to the page when this occurs.
This excess of vergence is commonly associated with an Accommodative Insufficiency. The eyes are aimed closer in than desired in an attempt to compensate for reduced focus stamina or focus ability.
This leads to a mismatch between vergence and focus, thus affecting binocular vision accuracy.
Management of convergence excess requires therapeutic spectacle prescription lenses to enhance the focus efficiency thus reducing the need to pull the eyes closer in.
This is a therapeutic treatment that requires monitoring over time to ensure the excessive demand is reduced to within a normal range of focus and convergence.
Usually over time prescriptions can be reduced and wearing time reduced. Without effective management, myopia (shortsightedness) can often result in later years, such as in high school.
This is also an eye coordination dysfunction, which involves difficulty with both eyes working to smoothly and efficiently track a moving object and to look from place to place. Children who have this dysfunction have difficulties with reading, such as loss of place, skipping lines, skipping words and lack of fluency and speed.
This is a focusing problem. Accommodation is how the eye changes focus from far and near objects. Shifting focus from far to near and near to far can be difficult. A typical example is when instruction comes from far away and then writing on a paper or computer is required.
This is difficulty with eye-hand coordination. It is challenging to process and reproduce visual images by writing or drawing, involving fine motor movements. Copying from the board becomes difficult and handwriting can be sloppy.
Difficulties with visual memory (inability to understand and recall what is seen), visual form perception (discriminate differences in size, shape, or form) and visualization (“seeing” in the mind’s eye) can show up in many forms.