Binocular Vision

What is Binocular Vision?

What we see is the result of signals sent from the eyes to the brain. Usually, the brain receives signals from both (bi) eyes (ocular) at the same time. The information contained in the signal from each eye is slightly different and with well-functioning binocular vision, the brain is able to use these differences to judge distances and coordinate eye movements.

How Does Binocular Vision Work?

Unlike some other animals, humans’ eyes are both set on the front of the face, permitting binocular vision. This forward-facing orientation of the eye means each eye has a rather similar view of an image. The field of view, which is the area that you can see when you close one eye, overlaps significantly between each eye also. The center of the eyes’ fields of view overlap with one another the most. This portion of the visual field provides the most detailed information to the brain. Visual information in the periphery or center of the visual field can, of course, be detected by one eye, but the combined visual information is what is required for binocular processing. This information is transmitted throughout a majority of the brain.

The Visual Pathway

Visual information is processed very early. Light (think of light as the image of an object) is focused by the eye onto the delicate neural structure of the retina. To simplify, think of the eye as similar to a camera. Like a camera, the eye uses a series of focusing mechanisms to place a clear image on the film (the retina).

The front window of the eye called the cornea, and the focusing mechanism called the crystalline lens, focus light onto the retina. The retina organizes the information (light) that lands on it and changes the information to electrical impulses. These impulses (also called signals) exit the eye through the optic nerve and begin the pathway through the brain. Shortly after the optic nerve exits the eye, some fibers of each optic nerve become intertwined. Visual information from different parts of the visual field are combined and the neurons continue to make their way through the upper and lower lobes of the brain (called the parietal and temporal lobes, respectively). The final stop of the neuron is the occipital lobe, an area of the brain in the back of the brain, which synthesizes and processes visual information. The end result is a single, coordinated image.

What is a Binocular Vision Disorder?

Binocular vision anomalies are among the most common visual disorders. They are usually associated with symptoms such as headaches, eye strain, eye pain, blurred vision, and occasionally double vision. There are many reasons binocular vision might become reduced or lost altogether, including:

  • Reduced vision in one eye
  • Loss of coordination of movement between the two eyes (strabismus)
  • Problems with the brain comparing images from both eyes

Binocular vision impairments often result in partial or total loss of stereoscopic vision and binocular depth perception. Conditions, where the eye is obviously turned or crossed, are commonly referred to with terms like "cross-eyed", "crossed-eyes", wall-eyes" or "wandering eyes". These binocular vision impairments are easily detected by others as all the observer needs to do is notice that both eyes do not aim in the same direction at all times. Some medical terms for these deviations or misalignments of the eye are strabismus, esotropia, exotropia, congenital strabismus, hereditary strabismus, pediatric strabismus, adult strabismus, accommodative esotropia, alternating esotropia, congenital esotropia, accommodative esotropia, esophoria, exophoria, exotropia, exotropic, esotropic, hyperphoria, hypophoria, hyperphoria, hypertropia. Other medical conditions which can contribute to poor binocular vision are anisometropia, astigmatism, nearsightedness, myopia, farsightedness, hyperopia, nystagmus, cerebral palsy, cataracts.

Some binocular vision impairments are not easily detected by parents, teacher or others because the turning or straying of the eye(s) is NOT obvious or consistent. Some eye turns are intermittent (they come and go) and/or they are not easily noticed by the untrained observer. A binocular vision problem is indicated, even when an eye turn is only occasionally visible. Convergence Insufficiency is a binocular vision disorder that is often overlooked because The tough thing about convergence insufficiency is that it often goes undiagnosed because a person can pass a typical 20/20 eye chart test and still have it. That's why early examination is so important.

Binocular Vision and Depth Perception

One of the reasons that binocular vision is so important is that it allows us to perceive depth and relationships between objects. Each eye sees slightly different spatial information and transmits these differences to the brain. The brain then uses the discrepancies between the two eyes to judge distance and depth. The result is the ability to see a 3-D image and distinguish the relationships between objects.

Without binocular vision, catching a baseball, driving or parking a car, making sense of classroom instructions on a blackboard or screen, and performing simple tasks such as walking or running becomes difficult. Those with impaired binocular vision often appear clumsy and uncoordinated because they lack the ability to orient themselves in relation to their environment.

Depth perception is technically called stereopsis or stereoscopic vision.

Symptoms Associated with Binocular Vision Disorders

Symptoms may include:

  • Dizziness, headaches and nausea
  • Unsteadiness while walking
  • Anxiety as a result of difficulty driving or reading
  • Anxiety as a result of too many stimuli in a large space or large group of people
  • Trouble concentrating while reading
  • Trouble with reading comprehension
  • Fatigue while reading
  • Restless sleep
  • Poor eye contact
  • Avoidance of work
  • Double vision
  • Motion Sickness

Often symptoms of ADD and ADHD appear similar to those of Binocular Vision Dysfunction and therefore can result in misdiagnosis.

In children, Binocular Vision disorders can cause significant problems in learning and doing school work. Parents often report having very smart children who just can't keep up with schoolwork or who will avoid schoolwork. Children with binocular vision disorders often experience double vision, words moving on the page when they read, blurry words on the page, etc. They may have to re-read sentences, thus slowing them down. They often do not know that what they are experiencing isn't normal. The frustration and anxiety from this can cause children to act out, disengage, or even go into depression. Detecting a binocular vision disorder early can prevent years of struggle for a child-- and their family alike. And, new research has proven that even adults can benefit from therapy for undiagnosed/uncorrected binocular vision disorders.

Diagnosis and Treatment for Binocular Vision Disorders

Fortunately, most problems with binocular vision are easily treated through eyeglasses, vision therapy, or surgery. Receiving a thorough annual optometry exam — especially during childhood when the visual system continues to develop — is essential to detect these eye problems. It is recommended that babies have a comprehensive vision assessment by an optometrist during the first year of life as early detection can improve outcomes and these skills are not evaluated by pediatricians.

References

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