Binocular Vision Dysfunction

We possess an incredible visual system that gives us the ability to see our world in three dimensions and judge distance with a great degree of accuracy. Each of our eyes is set a small distance from one another, and each sees an ever-so-slightly different image of the world, and your brain, by a process called fusion, blends these two images together to give one three dimensional picture or “depth perception.” Depth perception allows us to gauge the distance to, and dimensional characteristics of, an object. The remarkable ability to use both eyes together to produce a single, unified image, as interpreted by the brain, is known as “binocular vision.”

Vision disorders involving binocular vision occur when there is a failure of the eyes to work together properly, making binocular vision difficult or impossible. Signs of these disorders may include poor eye movement control, inability to properly focus, poor eye-hand coordination, and difficulty with motor skills, visual perception and eye-teaming abilities.

Vision is a result of the way our brain and our eyes interact with each other. We depend on our visual system to work properly in order to successfully read a book, copy words off the board at school, catch a ball, and tie our shoelaces. Let's use a normal, healthy 6 year old child about to learn to ride a two-wheeled bicycle as an example. The child has normal hardware (arms, legs, body, muscles, tendons etc.) but, up until now, has no experience – and therefore no software – to ride the bicycle. As he begins to ride for the first time he falls off. We know there is nothing wrong with his arms and legs he just needs to practice. It is this practice which is actually writing the software to ride the bike successfully. The change that takes place is in the software in the brain.

Vision isn't just what we see, it is how we interpret and interact with the information we receive from our environment. A person can have "20/20" vision and be able to read the smallest letters on the eye chart, but may still struggle with other visual symptoms such as: 

  • Intermittent blurred or double vision
  • Poor focus or attention, irritability, impulsiveness
  • Headaches and eyestrain
  • Eye and body fatigue from school or work
  • Squinting, rubbing or closing one eye
  • Poor hand-eye coordination
  • Difficulty changing focus from distance to near and back
  • Dizziness and motion sickness
  • Poor handwriting
  • Loss of place, repetition, or omission of words while reading
  • Letter, number and word reversals
  • Difficulty with reading comprehension; avoiding reading

Binocular vision dysfunctions can sometimes be difficult to detect, even with a comprehensive eye examination with your primary care optometrist, and additional testing is often required by an eye care professional who specialized training to properly evaluate the following areas of your visual system:

  • Eye Tracking (Ocular Motility) Testing – A measurement of fast small eye movements called saccades and smooth, fluid movements called pursuits.
  • Eye Teaming (Binocular Vergence) Testing – A measurement of coordination, convergence, and divergence of the two eyes.
  • Eye Focusing (Accommodation) Testing – A measurement of automatic eye focusing relating to the clarity of near vision and sustained near visual attention.
  • Visual Discrimination – The ability to see similarities from differences.
  • Visual Memory – The ability to visually remember the characteristics of a shape/object after a brief presentation.
  • Visual Spatial Relationships – The ability to see the difference among forms based on orientation.
  • Visual Sequential Memory – The ability to remember a series of forms in their specific order of presentation.
  • Visual Figure-Ground – The ability to perceive a form visually, and to find this form hidden in a clutter of a distracting background.
  • Visual Directionality – The ability to identify language symbols based on their directional orientation.
  • Visual Motor Integration – The ability to analyze visual information and reproduce the response in a paper and pencil task.
  • Visually Directed Gross Motor Function – The ability to effectively integrate the two halves of the body.
  • Visual-Vestibular Integration – The ability to integrate the visual system and the vestibular system.
  • Baseline reading tests – Standardized testing of word recognition and fluency.

When someone has difficulty with their eye teaming it can make every day tasks incredibly challenging. It may be something that you've struggled with all your life or perhaps you recognize these symptoms in a family member. Vision therapy can help you or your loved one to overcome their visual dysfunctions and lead more happy, productive lives. 


Learning-Related Vision Problems

Over 80% of learning is visual.

Vision problems can cause significant behavioural and learning challenges for children. A learning-related vision problem directly affects how we learn, read, and sustain close work. Visual dysfunctions can manifest in ways that are often confused with dyslexia, ADD, ADHD, and other learning disabilities because they affect a child's ability to focus for reading and school work.   

Everyone knows a child who just can't or won't sit still long enough to read a sentence in a book, and who therefore avoids it at all costs. In some of these cases their vision may not even be blurry (or require corrective lenses), but it may be distorted, they may see double, or the words may move around on the page, making it tremendously difficult for a child to focus and read a word, let alone a whole book or sentence.

25% of school-aged children have vision problems that are affecting their learning.

If your child is having difficulty with learning, you should be sure to take them to an optometrist that specializes in vision therapy and learning-related vision problems for a functional binocular vision assessment. Our optometrists will assess the entire visual system including the 17+ visual skills used in reading and daily life, such as the ability to smoothly move your eyes across a sentence, your ability to hold your focus on a point in space, and the ability for your eyes to work together as a coordinated team with your brain.

3 in 4 children with reading disabilities have underdeveloped visual skills.

Does your child experience any of the following symptoms: 

  • Headaches or eye strain
  • Blurred or double vision
  • Losing their place while reading, skipping, or re-reading lines
  • Reversing letters/numbers/words
  • Poor hand-eye coordination
  • Clumsiness
  • Fatigue from school
  • Squinting, rubbing or closing one eye while reading
  • Poor word/letter recognition
  • Poor spelling
  • Poor handwriting skills
  • Motion sickness
  • Poor attention and concentration

Infant Development

Childhood is full exciting experiences that prepare us for the future. Reading is an example of a skill that develops over time. We aren't born knowing how to read. Similarly to how a child must learn how to crawl before they can walk before they can run, the eyes must learn to move smoothly and accurately together as a team before a child can learn to read.

There are specific developmental milestones that should occur from 6 months to 4 years of age. Infants are born with very basic reflexes that help to guide them through early development. These reflexes are automatic motor movements that help infants survive, such as the sucking reflex for feeding. During normal development, infant reflexes are integrated and become voluntary movements. If they are not integrated properly, called retained primitive reflexes, they may impede further development. These retained primitive reflexes can often be found in children who have difficulty with learning and reading.


Traumatic & Acquired Brain Injuries

Eyesight (visual acuity) is measured by reading the small letters on an eye chart. After a traumatic or acquired brain injury you may be told that you have "20/20" vision, but there is more to vision than simply being able to see those small letters. Vision occurs in the brain, not in the eyes. You can have healthy eyeballs, but have significant difficulty with your vision.

The light and visual information that your eyes collect is transported through many different areas of the brain, including the frontal cortex, the midbrain, the occipital cortex, and more. Throughout this process, there are an incredible number of connections that are made between your visual system and your other sensory areas like touch, hearing, and balance. Important information travels back and forth between these areas through these vital connections. 

When a person suffers a brain injury, such as a concussion, whiplash, or stroke, these vital communication pathways can be severely affected. Many brain injuries result in significant visual symptoms due to the disruption of these neuro-visual connections.

More than 50% of our brain is involved in vision. Upwards of 90% of people who fail to recuperate on their own from a traumatic brain injury have a neuro-visual dysfunction, and have visual problems that cause headaches, light sensitivity, double vision, eye strain or blurred vision.

Anyone who has suffered from a brain injury should be seen by an optometrist who has specific training and experience with eye and vision problems related to brain injury. They will perform a comprehensive and specific evaluation that will include testing of your: eye health, focussing abilities, eye teaming abilities, eye muscle movements, depth perception, visual fields (classic and functional), visual perception and processing skills, visual impact on balance and posture.

Visual Symptoms of a Brain Injury:

  • Headaches or eye strain
  • Blurred or double vision
  • Losing your place while reading, skipping or re-reading lines
  • Poor hand-eye coordination
  • Fatigue from school or work, particularly reading and computer work
  • Squinting, rubbing or closing one eye to avoid eye strain or double vision
  • Light sensitivity
  • Dizziness
  • Loss of visual field or peripheral vision
  • Visual perceptual difficulties, including visual memory
  • Balance problems
  • Avoiding crowds and visually busy environments like grocery stores or malls

Even though general rehabilitation with a physiotherapist, chiropractor, or occupational therapist may include balance, eye-hand coordination, and visual tracking treatments, these limited forms of treatment with these professionals do not typically address the majority of visual problems following a concussion. Brain injuries are a multi-faceted problem and require a team of professionals to help rehabilitate.


Strabismus & Amblyopia

"Lazy" Eyes and Eye Turns


Amblyopia or "lazy eye" is a neurological developmental vision problem that occurs during infancy and early childhood. When a person has difficulty using both eyes together as a team their brain may begin to ignore the visual sensory information from one eye to avoid confusion or double vision. This is called suppression. When an eye is suppressed, it's development is impaired so that vision in that eye cannot be corrected optimally even with glasses or contacts. This lack of development of vision is called amblyopia. 

Amblyopia can be caused by an eye turn (strabismus), a significant amount of uncorrected farsightedness, nearsightedness or astigmatism, or something blocking the vision such as a cataract or tumour. People with strabismus or amblyopia often do not have full stereoscopic depth perception because both eyes are not being used together. Left untreated, amblyopia can affect a child's self-image, work, school, sports, relationships, and may also lead towards depression. 


Strabismus is a condition where a person's eyes do not align at the same point in space at the same time. The affected eye often appears as if it is turned inwards (esotropia) or outwards (exotropia). Sometimes both eyes will take turns being misaligned. The turned eye can be present all of the time or only sometimes, such as when the person is tired or sick, or when they are concentrating on something. Strabismus affects 5-8% of the population. It is not always obvious to parents, and the child is often unaware. Having a turned eye can mean that the person sees double, but in many cases, the brain will suppress the turned eye so that the person does not experience the double vision, thus resulting in amblyopia.

When Does It Happen?

Different types of strabismus can first occur at various times in life. Any new eye turn should be assessed by your optometrist because some eye turns can be a sign of a disease. Usually the amount of strabismus and the severity of the amblyopia are dependent on the age the deviation begins, and how long before it is diagnosed. Some can occur between birth and 6 months of age, while others tend to occur between 18 and 36 months of age, including amblyopia without an eye turn (due to a large difference in the prescription between the two eyes). 

This is why all children should have their first eye examination at 6 months of age. Parents often won't know their child has a vision problem, as the child rarely complains and often seems to be functioning well.

By the time the child reaches school-age, the condition has been significantly engrained and is harder to rehabilitate, but don't worry, all hope is not lost! Sadly, many professionals may tell parents that nothing can be done once a child reaches the age of 7, or that surgery is the only option. The newest research has proven this to be false!


Until the newest research advancements, Patching was often recommended by many optometric professionals. Though patching can be effective at improving the visual acuity in the strabismic or amblyopic eye, the effect is often temporary because it does not teach the brain how to coordinate the eyes to work together as a team. This is where vision therapy can help! 

While surgery is sometimes necessary in early onset, large deviations, surgery rarely solves the problem with one operation because the problem is not with an eye muscle, it is with the brain! This is also why many people end of undergoing multiple surgeries, because the eye starts turning again since the brain still doesn't know how to properly team both eyes together. Often the goal of surgery is simply cosmetic, and it is not able to achieve good visual acuity or depth perception on its own. 

Neuroplasticity research has shown that optometric vision therapy can provide the necessary, meaningful visual experiences for individuals of any age to begin to learn to use their two eyes together as a team. 

In many cases, strabismus and amblyopia can be resolved without the need for surgery or extensive patching. Many patients will continue to see their vision improve after their in-office vision therapy program as been completed.


Special Populations

Autism, Cerebral Palsy, Special Needs

Patients with autism can show an array of vision based behaviours such as poor eye contact, lateral peering and waving stimulating objects like their hands – in front of their eyes. There is the assumption that these behaviours are not treatable when perhaps they are instead caused by an underlying treatable vision condition. If an underlying vision condition is found to account for some or all of the vision based behaviours, it may be helped with vision therapy.

Patients with cerebral palsy have a lack of muscle control due to brain damage near the time of birth. Conditions such as strabismus can be related to poor muscle control in the eyes. Vision therapy can be a non-surgical means of helping these patients achieve better visual function and cosmetic appearance by treating the underlying muscle control problem. Poor muscle coordination does not always result in a strabismus; it can also affect the ability to focus and to track properly. Vision therapy improves muscle coordination and control which can help with better acquisition of visual information and improve their development and quality of life.



Vision is very important to the success of many athletes as hand-eye coordination is vital to one's sports performance. Vision guides motion, and motion impacts vision. Sports vision therapy is unique to the athlete’s sport of choice and the specific demands of their sport. In practice, no-one has developed the ultimate visual process; however many have developed exceptional visual abilities beyond the normal range. Elite athletes are an excellent example. The difference between the average athlete and the elite athlete most often is in the difference in their visual abilities. Their excellent visual processing derives meaning from the environment rapidly and efficiently so their performance is increased well beyond the abilities of those around them.

Areas that will be explored include: hand-eye coordination, dynamic visual acuity, peripheral vision, depth perception, visual reaction time, tracking and focus ability. These are some of the vital visual skills needed to be a superior athlete, and it has been proven that athletes with excellent visual function show greater success in their chosen sport. Professional athletes in a variety of sports have used vision therapy to bring their game to the next level. 

Sports vision training helps the athlete improve many vision and motor abilities necessary to increase performance, including:

  • Dynamic visual acuity helps improve the athlete’s ability to see things clearly while in motion or helps the athlete track moving objects.
  • Eye-hand coordination determines how well the athlete coordinates control of their eye movement with their hand movement. Improving this skill increases the athlete’s ability to guide reaching, grasping, passing, and hitting within their sport.
  • Eye focusing (also known as accommodation) refers to the strength, flexibility, and accuracy of the eye focusing system. Accommodative skills allow the athlete to keep objects in focus as well as quickly change focus during the game.
  • Peripheral vision refers to our side vision. Improving peripheral vision helps the athlete see objects outside of their focal point. Improving peripheral vision gives the athlete a wider view of the field.
  • Visual tracking is the ability to move our eyes from spot to spot while maintaining focus on the object we are looking. Improving visual tracking advances the athlete’s reaction time, speed, and fluidity within their sport.
  • Visual reaction time refers to the amount of time it takes for environmental stimuli to travel from our vision system into our motor system to produce a physical reaction. Improving visual reaction time helps the athlete hustle up their response time, by training the brain to work more efficiently.