Right Or Left - Does One Side Of Your Brain Control Your Vision?
By Essilor News
Much of the human brain is arranged in a way that the right half of the brain controls the left half of the body and vice versa. For example, information about touch and pain coming from the right half of the body goes to the left hemisphere of the brain; and muscle movements of the left side of the body come from the brain's right hemisphere.
But the eyes are an exception to this rule. Since we have two eyes we have two optic nerves that eventually meet at the optic chiasm, centrally located near the pituitary gland. At this point, each nerve then splits again so that both halves of the brain receive information from each eye.
Sight is a complex function of the brain that extends from the front to the back of the head. To produce sight, the eyes capture information and send it through the optic nerve to be processed by the occipital lobe.
Each eye sees a part of the outer world which is called its visual field. The total visual field is the sum of the right and left hemi-visual fields in each eye. Just like the visual field is divided into two hemi-fields, the retina, a layer of cells at the back of the eye, is divided in half.
The most important fact is that the lens of the eye inverts the image that forms on the retina; therefore, objects seen to our left are sensed by the right half of our left eye. In other words, light coming from anywhere in the left half of the visual environment projects onto the two right half-retinas, and the information is sent to the right hemisphere.
This arrangement means that when are looking at something, each of the two retinas are seeing the same thing, providing binocular 3D vision.
A massive stroke in the left side of the brain leads to paralysis and lack of sensation in the right side of the face, right arm, and right leg. What is less commonly known is that such a stroke can also lead to blindness in the right half of the visual world-the right visual field-involving both eyes.
Problems with sight, such as vision gaps, are also divided along these lines. A complete right homonymous hemianopia (neurologists call this half-blindness) actually dissects precisely the center of gaze. For instance, if you look at the word "was," focusing your gaze on the "a," you wouldn't see the "s" - and you would only see the left half of the "a."
We can see from such tests that each eye sends information to both hemispheres, and conversely, that each hemisphere of the brain gets input from both eyes. So it is more accurate to say that each hemisphere of the brain is dealing with the opposite half of the environment, rather than with the opposite side of the body.