We see a slightly different picture from each eye and our brain should be able to put those two together. In order to be able to use visual information as efficiently as possible, we need to be able to use our two eyes together, as a team. When they work together we can begin to have depth perception (3D) and can easily track across a page to read text.
Binocular Vision is the ability to use the two eyes together as a team. Binocular Vision Dysfunction (BVD) means that we don’t have that ability. Vertical Heterophoria means that the line of sight from one eye is higher than the line of sight from the other eye.If the two eyes do not line up together, either horizontally (side to side) or vertically (up and down), it is hard to put the two different pictures together in order to see one unified image. It is then difficult to perceive depth or see a 3-dimensional mental picture. Tracking an object that is moving or reading lines of print also become more difficult or tiresome. So much energy is being used to simply line up the eyes that there is not enough energy left over to understand what was read.
People with BVD often have symptoms such as headache, vertigo, and dizziness. This is due to a mis-match between the visual system (what we see) and the vestibular (balance) system in the inner ear. These people may have balance problems, may be clumsy, feel motion sickness, or become nauseous. Especially if someone has had a concussion, a brain injury, or a stroke, they may complain of “brain fog” or “eye fog”. BVD often leads to reading and learning related problems.
Most people who have these problems do not realize that the root source of their problem is in the visual system.
There are 6 muscles that move each eye.
- 2 of the 6 move the eyes from side to side (horizontally).
- 4 of the 6 muscles move the eyes up and down (vertical).
If the 2 eyes don’t perfectly line up, it is difficult to have the image from each eye to come together to make one picture inside the brain. Some people then tilt their head in an attempt to re-align their eyes. Doing so for a long while can lead to neck pain and headaches. We constantly move our eyes. Objects are obviously not only in the straight ahead position, as might be tested in the examination chair at the eye doctor’s office. Our brain must constantly adjust the signal sent to our eyes, depending where our head position is and whether the object we are looking at is directly in front of us, to either side, or above or below eye level.
Prism prescribed in eyeglasses may be a first step, and may give short term relief, but at times, the prism alone does not solve the problem. The reason for that it is that the prism compensates; it does not correct. Vision Therapy enables people who have misalignment of the 2 eyes to develop the visual skills needed to align them. Once this ability is gained, the problem is solved. Eyeglasses alone often can’t fully solve a problem of the two eyes being out of alignment.
The brain analyzes the visual information that comes into it (afferent) and then controls where we point our eyes (efferent). When there is a misalignment, some eye surgeons recommend eye muscle surgery. Unfortunately, surgery can often makes the problem worse. The brain, and not the eye muscles, is where we bring the picture from each eye together. Surgery rarely solves the problem because it does not address the visual processing. Vision Therapy addresses the visual processing occurring in the brain.
Once someone learns the visual skills of where to point their eyes, how to use the two eyes together as a team, how to move the eyes and how to hold it there, they sustain those skills. It is similar to learning to ride a bicycle or driving a car. Once someone has learned the skill, they retain the skill even if they had not done so for years. Vision and visual processing is a skill that can be taught efficiently, learned, and maintained.