Binocular Conditions

Binocularity

Generally, human beings come equipped with two eyes and one head. Because the two eyes are located in different positions in the head, each eye takes a unique view from its own perspective. With two different side by side perspectives, we're able to see a little bit around solid objects without moving our heads. So while the views from the two eyes have a lot in common each eye picks up visual information that the other doesn't. Each eye captures its own image and the two separate images are sent to the brain for processing. Remember you see the world from two points of view!

When the two images arrive simultaneously in the back of the brain, they are united into one picture. The mind combines the two images by matching up the similarities and adding in the small differences. The small differences between the two images add up to a big difference in the final picture! The combined image is more than the sum of its parts. It is three-dimensional vision.

Stereoscopic Depth Perception

The word "stereo" comes from the Greek word "stereos" which means firm or solid. With stereo vision you see an object as solid in three spatial dimensions-depth, height, and width. That's why we call it 3D. It is the added perception of the depth dimension that makes stereo vision so incredible.

Stereoscopic depth perception probably evolved as a means of survival. With two-eyed depth perception we can see where objects are located with much greater precision, especially when those objects are moving toward or away from us in the depth dimension. And because stereoscopic depth perception helps us perceive small differences in a visual field of many similarities, it's our best tool for decoding or "breaking" visual camouflage. Thanks to this visual ability, our ancestors could spot a lion hiding in the brush or a poisonous snake coiled on a branch.

Nowadays, most of us don't have to worry about lions in the brush. But we use our stereoscopic depth perception to drive a car, catch a ball or swat a pesky mosquito.

Why are some people unable to see 3D?

In order to see 3D you need two eyes that work together as a coordinated team. Problems with binocular coordination- the successful teaming of the two eyes, can make three dimensional viewing difficult.

Less than 5 percent of the population have visual disabilities that make binocular coordination extremely difficult or unattainable. This group includes those who have lost an eye or those who have amblyopia (lazy eye) or strabismus (eye turns).

Types of Binocular (Eye Teaming) Problems

Convergence Excess (Overconvergence)

Convergence Insufficiency (Under convergence)

• Convergence Insufficiency - (clinical condition) the inability of the eyes to turn inward and/or sustain an inward turn. Symptoms include eye strain with reading and using a computer, headaches, loss of comprehension, difficulty concentrating, blurred or double vision, and eye fatigue. Clinical signs include: near point of convergence of greater than 4 inches (10 cm), greater exophoria at near than at distance, and low AC/A ratio. Vision therapy is an effective treatment option.
• Convergence Excess - a clinical condition in which the eyes have a tendency to turn excessively inward when viewing an object at a near distance. Symptoms may include visual fatigue while reading or using a computer, occasional blurred or double vision, and inability to comprehend or concentrate while reading. Clinical signs include: greater esophoria at near than distance, high AC/A ratio, and a high lag of accommodation. Can be improved with vision therapy and/or glasses.
• Fusional Vergence Dysfunction - inability to efficiently utilize and/or sustain binocular vision. Symptoms include eyestrain, headaches, decreased comprehension, inability to concentrate while reading, excessive tearing, and blurred vision. A patient will have difficulty with both base-in and base-out prisms. Vision therapy is an effective treatment option.
• Esophoria - a tendency of the eyes to want to turn more inward than necessary when an individual is viewing an object at near or at distance, which may cause the individual to experience eyestrain and other symptoms. Symptoms of basic esophoria include: eyestrain, headaches, blurred or double vision, apparent movement of print, and difficulty concentrating on and comprehending reading material. Clinical signs of basic esophoria include: AC/A ratio is normal, equal esophoria at distance and near, and normal near point of convergence. Sometimes esophoria is caused by a refractive error such as hyperopia (farsightedness), and glasses or contacts can correct the problem alone. However, sometimes vision therapy is needed to to help re-train the eyes to function more appropriately.
• Exophoria - a tendency of the eyes to want to turn more outward than necessary when an individual is viewing an object at near or at distance, which may cause the individual to experience eyestrain and other symptoms. Symptoms of basic exophoria include: eyestrain, headaches, blurred or double vision, apparent movement of print, and difficulty concentrating on and comprehending reading material. Clinical signs of basic exophoria include: normal AC/A ratio, equal exophoria at distance and near, and decreased near point of convergence. Vision therapy is an effective treatment option.