VISUAL EFFICIENCY PROBLEMS
Visual efficiency problems affect the way that the eyes work, and might make it more difficult, tiring, or uncomfortable to perform certain visual tasks, such as reading, driving, playing sports, or attending classes, meetings, and presentations. Below is a list of the main visual efficiency problems. Click on any one to learn more about it.
EYE TEAMING PROBLEMS
In order to see properly, our eyes have to work together in a precise and coordinated fashion.
Every time we look at something, we must accurately aim the two eyes directly at the object of concern. Each eye sends an image to the brain, which then combines these two images to make one “fused” image. If these images are correct, the result is clear, single vision, and a perception of depth. If, however, the eyes are not performing in a coordinated manner, the brain will receive two different images and will experience double vision or blurred vision.
As you can imagine, double vision is not something a child or an adult can tolerate. It becomes very difficult to function at school, play, or work if double vision occurs.
The two most common types of eye teaming problems are:
Convergence Insufficiency: In this eye teaming problem the individual has poor ability to bring the eyes in toward the nose when reading or doing close work. If the eyes actually drift out, the person experiences double vision. To control the eyes' tendency to drift out, the individual must exert excessive effort to make the eyes turn back inward.
Convergence Excess: In this eye teaming problem the individual has poor ability to bring the eyes out away from the nose when reading or doing close work. If the eyes actually drift in, the person experiences double vision. To control the eye’s tendency to drift in, the individual must exert excessive effort to make the eyes turn back out.
Eye teaming problems actually have more of an impact on learning or performance at work or school than unclear vision. Unfortunately, most school vision screenings are only designed to detect unclear vision. Very few school screenings even test for eye teaming disorders.
EYE TRACKING PROBLEMS
The eyes must move accurately, smoothly, and quickly from word to word or from one target to another. Every time a child looks from the board to a book, for instance, the eyes must accurately jump from one target to another. The same is true for reading.
An eye tracking problem is present when someone cannot perform this function with adequate facility. The visual system, even if generally healthy, may not have developed as expected. Tracking, in such a case, is inaccurate, slow, and may interfere with reading and school or work performance.
Someone who has good decoding skills and a normal sight vocabulary may still experience problems when reading for comprehension. If the eye tracking system is not functioning properly, the information received by the brain does not accurately represent the information in the book or on the board.
A good analogy is to compare the eyes to television cameras sending information to the television. The television can only display what the camera records at an event, so if the camera isn't moving quickly and accurately enough, the television will not display the event properly. In the case of the human visual system, the eyes are the cameras and the brain is the television. The information received by the brain is only as accurate as what the eye captures as it moves from one object to another.
The three types of eye tracking problems are:
Fixation Dysfunction: This is the inability to direct and maintain steady visual attention on an object.
Deficiency of Saccades: This is the inability to move the eyes smoothly from point to point, which is necessary when reading.
Deficiency of Pursuits: This is the inability to efficiently track a moving object, such as a ball rolling across a table.
These problems tend to occur together and are jointly called oculomotor dysfunction.
EYE FOCUSING PROBLEMS
We have to change the focus of our eyes every time we look from one object to another. Most people are not aware that we have to focus our eyes because it feels like it happens automatically.
We adjust our focus with the help of a muscle in the eye called the ciliary muscle or "focusing muscle." When a person looks from the board to a book, for instance, this muscle must contract, which changes the shape of the lens in the eye and allows the person to see the print in the book clearly. When the person wants to look back to the board, the focusing muscle must relax, which permits clear vision at distance.
A focusing problem occurs when someone is unable to quickly and accurately constrict or relax the focusing muscle, or if someone is unable to maintain this muscle contraction for adequate periods of time.
The three most common types of focusing problems are:
Accommodative Insufficiency: This is a condition in which an individual is unable to contract the focusing muscle for adequate periods of time.
Accommodative Excess/Spasm: This is a condition in which an individual contracts the focusing muscle more than necessary or has difficulty relaxing the muscle; it is similar to a muscle spasm.
Accommodative Infacility (Inflexibility): This is a condition in which an individual has difficulty with both contraction and relaxation of the muscle.
Studies have found that over 50% of concussion patients have associated vision problems. The part of the brain that controls vision is a complicated system, so even a mild concussion can cause vision-related symptoms, such as blurry vision, focusing problems, headaches, difficulty in crowds or large spaces, sensitivity to light, concentration or memory problems, and fatigue.
When a person suffers a concussion, it is important that he or she be assessed early for any visual problems. This assessment should be performed by an optometrist who has training and clinical experience in caring for patients with vision problems due to brain injuries. The doctor should be residency trained and a member of the College of Optometrists in Vision Development (COVD).
The brain is a soft organ, and it needs time to rest and recover after an injury. Many vision problems associated with a brain injury can initially be treated by prescribing or adjusting lenses in a patient's glasses. Often this will be enough to alleviate symptoms. But when visual symptoms persist, simply resting might not be sufficient to restore normal visual function. In these cases, neuro-optometric rehabilitation (vision therapy) can be a very effective way to treat visual problems related to a brain injury.
Amblyopia is a condition in which vision in one or both eyes cannot be corrected to 20/20 even after the correct eyeglasses have been prescribed. In a child with normal visual development, the brain receives information from both the right and left eyes and combines the two to see one clear picture of the world. This “combining” of information from both eyes is called “fusion.” Amblyopia occurs when the brain is ignoring or “suppressing” information from one eye. This leads to a lack of development or deterioration of vision in the eye not being used.
Amblyopia is caused by strabismus (crossed eye or wall-eye condition) or by unequal optical prescriptions in the two eyes. Generally, amblyopia will develop in children only if the causative problem starts before the age of seven. Fortunately, amblyopia can be treated at almost any age; however, the earlier the detection, the better the outcome.
Another term that is sometimes used by the public when referring to amblyopia is “lazy eye.” This is not the best way to think about this condition. The eye is not lazy; rather, because of the differences between the two eyes, the brain cannot fuse information from both eyes and shuts off or ignores information from one eye.
The three most common types of amblyopia are:
Anisometropic Amblyopia: This is a condition in which the eyes have very different prescriptions. One eye, for example, may be very farsighted while the other is only slightly farsighted.
Isometropic Amblyopia: This is a condition in which the prescription is very high in both eyes. The child’s vision will be poorly developed in both eyes due to the need for glasses.
Strabismic Amblyopia: This is a condition in which one eye is either turned in or turned out at all times. The brain suppresses the images coming from the turned eye, leading to a deterioration or lack of vision development in that eye.