There are many technical terms for problems of the eye functioning. Many sound like horrible diseases, but don't let them frighten you. Most are problems with efficiency and can be trained with therapy.
Convergence Insufficiency or Excess
When an object is getting closer to you, your eyes have to converge to see it. Converge means to move the eyes in towards each other.
Double vision is a common side effect of poor convergence ability. Convergence is the ability for the eyes to turn inward towards each other. This is important for all near tasks. See if you notice... look in the distance across the room. Now hold a pen in front of your head around 12 inches from your nose. Look from across the room to the pen. Do you feel your eyes turning in? Now pull the pen towards your nose... how close can you bring it before it becomes double?
Many times the ability to converge the eyes is overlooked in eye exams. This is a very key item in reading, and near vision tasks. Do you ever get tired and feel difficulty in "focusing" at a book or computer screen? Do you ever feel like you see double at near? This is due to poor eye alignment. Poor alignment can cause headaches, due to a strain to keep your eyes aligned. This same near stress can decrease concentration, and reading accuracy. Attention deficit disorder is heavily linked to this ocular stress.
Convergence Insufficiency has a very high success rate in therapy. Most people can have marked improvement after two weeks, noticing less eyestrain, headaches, better attention. Most cases can be alleviated in 3-6 months, depending on the motivation of the patients.
Focusing is the more common name of this category. The closer something is to your eyes, the more you need to focus. Likewise, the further the object the less you need to focus.
Blurry vision, fluctuating vision, headaches, decreased distance vision after near work, attention problems, are all examples of having difficulty focusing your eyes. Accommodation is the ability to focus (flex your natural lens inside your eye), and the ability to relax the focus.
Accommodation can have the tendency to spasm. For instance, if you read or focus at near for long periods of time, you may have difficulty relaxing your eyes to see clearly in the distance. If the eyes are not properly evaluated by your eye doctor, instead of relaxing your eyes, a prescription for distance may be given. This my initially clear the distance vision, but now you need to over-focus your eyes to see in the distance when the should be relaxing. In addition to the over-focusing in the distance, now when you go to read with the glasses on, you need to strain your eyes even more to see clearly. This strain may cause your eyes to become blurry in the distance again, and thus need new glasses for the distance. This can become a vicious cycle, and your glasses may become thicker, and thicker, and thicker.
This is why many times when a person becomes a forty year old, this distance prescription for their glasses may start to decrease. This is due to the loss of ability to focus the eyes slowly. As the eyes relax, the vision becomes clearer with less power in the lenses. Vision therapy can help teach a person to relax his/ her eyes efficiently to avoid the over-focusing that can occur.
Divergence Insufficiency or Excess
This is the opposite of Convergence. Divergence means to move the eyes out away from each other and usually occurs when looking at an object moving further away.
Divergence is the opposite of convergence. When your eyes diverge, they are turning away from each other. So if you are looking 6 inches from your nose at the tip of a pen...then your eyes will need to diverge to see far away. Divergence excess means the eyes turn out too much when looking in the distance...this creates a problem for the patient. The patient will either see double when looking far away, or suppress an eye (shut an eye off).
Likewise, divergence insufficiency means the eyes do not spread apart enough to see in the distance. When the patient is looking far away, the eyes may appear crossed, or one eye may appear turned in slightly. Again, either one eye will shut off or the patient may see double.
Eye movements use the Ocular-Motor muscles. Reading, sports, balance, depth perception, and virtually everything requires good eye movements.
Very common problem in people of all ages.
This mechanism is a persons ability to move their eyes. If not efficient, a person can have difficulty reading (losing their place, or repeating the same sentences). People with this condition may also have difficulty with balance, depth perception, sports, or hand eye coordination.
The eyes need to function with essential two important eye movements:
Pursuits - the ability to follow a slow moving object with the eyes accurately.
Saccades - the ability to jump your eyes from one target to another accurately.