Intro to Vision Skills
Is seeing clearly (20/20) really enough?
Did you know that being able to see clearly is only a small part of what makes up your vision? In fact, there are closer to 17 different visual skills necessary for healthy vision. Seeing 20/20 is just one of these skills.
The other skills include areas such as how the eyes work together, how accurate and efficient movements are, and how the incoming visual information is processed. In fact, we are not born with all of these visual skills in place, they are learned and developed over time.
85% of classroom learning comes through the visual system.
Poor visual skills can lead to difficulties with reading, learning, overall school performance and even sports. This happens when a good visual foundation is not developed properly and stress causes the unstable system to break down under too much load.
Visual skills can also be influenced by many physiological, environmental and psychological factors such as development, disease, infection, nutrition, fatigue, environmental stress, emotional stress, opportunity, attention and attitude. Some individuals are better than others at compensating for these influencing factors.
Fortunately, vision therapy can help patients to use their visual system more efficiently and automatically by building neural pathways at any age, so they will be better equipped to handle heavier loads on their visual system. This can be achieved through vision therapy. At our Opto-mization™ Neurovisual Performance Centres, we are pleased to offer testing and treatment for a variety of these conditions.
Understanding Visual Input, Put-Put, and Output
To better understand how to fix visual problems, we need to understand the visual system. For sake of discussion, the visual process can be broken down into the following categories:
We can break down visual skills for the sake of definition, however, it is important to realize that these skills coordinate together almost simultaneously. The neural pathways of vision are highly interconnected, which is why 2/3rds of the brain pathways are involved with vision, while the other 1/3 is all the other senses combined.
Visual Input Skills
If you don’t get correct information input, how can you get good output?
A good analogy is having a television that works really well, but the antenna is broken. The broadcast of the information has a lot of noise and causes poor reception. If the visual system has a lot of noise coming in due to inefficient input skills, it will affect how we perceive and process the information to derive meaning from it.
Visual acuity is a measure of the sharpness of eyesight, or how clearly you see. It is influenced by eye structure, stress and the focusing system. It is the ability to identify a shape of a certain size at a certain distance, however, it gives no information on whether or not meaning is obtained from what is seen. The Snellen fraction (20/20, etc.) is most often used in an exam to measure visual acuity. Though most of the time, doctors try to get their patients to see 20/20 or better, there are particular circumstances where greater visual function is best achieved with a less clear image.
One common factor that can negatively influence visual acuity is refractive error.
Refractive error is caused by how the light is bent into the eye. Myopia (nearsightedness), Hyperopia (farsightedness), and Astigmatism occur when the shape of the eye is not ideal enough for the light rays to fall on the fovea (the only place the image can be seen sharply). To learn more, visit the refractive error section.
Other causes of decreased visual acuity are ocular disease or amblyopia (lazy eye). Even if there is no significant pathology or power difficulties, a person can have difficulty seeing clearly because of an inefficient accommodative (focusing) system.
Keeping an image clear at all distances is a factor in visual input.
Assuming the eye is healthy, it is the accommodative system that actively keeps an image clear at various distances (switching easily and effortlessly between distance and near), as well as sustaining clarity at the target, especially up close, for long periods of time.
Accommodation is difficult to “see,” just like it is difficult to see an automatic camera focus, but we can calculate how much is needed at certain distances. Remember, the nearer the distance of interest, the more power we need from our focusing system.
If a person is farsighted or nearsighted, the refractive power changes the amount of accommodation needed to see up close clearly.
The farsighted person’s eyes are typically more comfortable focused in the distance and must work much harder to focus at near. Children are expected to be a tiny bit farsighted through much of elementary school with the amount of farsightedness decreasing with age. A lot of farsightedness, however, and its known effects on accommodation, combined with hours of daily desk work, can result in signs and symptoms affecting academic achievement for students.
A person who is nearsighted needs to use less power at near than someone who is farsighted because their eyes are already “preset” to focus more closely.
Keeping an image single is another factor in visual input.
This is controlled by the vergence system. Vergence is how you move your eyes in or out to look at objects at different distances. If your eyes are not coordinated together well and pointing in the same place, you can experience double vision. This can not only cause confusion, but could lead to misalignment of the eyes (phorias), noticeable eye turns in or out (strabismus), having your brain shut down an image (suppression) and can lead to your brain disregarding most of the information coming from one or both eyes (amblyopia).
Any of these conditions can cause symptoms such as eyestrain, fatigue, avoidance and headaches. If you notice a child having these symptoms, you should refer them to a behavioral optometrist for a comprehensive developmental vision exam.
You can actually watch someone use their vergence system by having a friend look over your shoulder at an object in the distance. If they have do not have any eye turns (strabismus), both of their eyes should be looking straight ahead. Now ask your friend to look at the end of a pencil held approximately 1″-2″ from their nose. Did you notice how both of their eyes turned in? This cross-eyed appearance is called convergence. Now have them look back out at the distant object. Did you notice how their eyes went back out again? This outward movement of your eyes is called divergence. This ability can be measured by your eyecare provider.
Accommodation and vergence working together
These two systems (along with your pupil that changes size to allow the proper light to come in and helps with depth of focus) ideally work together to keep images you are attending to clear and single.
You can think of accommodation as finding the distance at which to focus (defining the plane focus), while vergence defines the point of focus within the plane. The closer we want to focus and point our eyes, the more “power” or effort we need to do so.
It is important to have effortless control over these systems so when the going gets tough and you need to work a little harder, you can! It is also important this process is automatic.
Accommodation and vergence should work hand in hand with liberal degrees of freedom between the two to help bring you clear and single images. If an individual exhibits extra effort to maintain single and clear vision, symptoms usually worsen over time. Unfortunately, some people (especially kids!) can develop adaptation strategies to cope with these problems, like avoidance or amblyopia, so they may end up not having a variety of vision symptoms.
If these two systems are not working smoothly or efficiently together and one system is working too hard or not hard enough, the result is a visual system that fatigues and basically breaks down after short periods of visual stress. Usually this results in the brain fighting between either keeping the image clear, but double or keeping the image fuzzy and clear.
Eye Coordination – Binocularity
Eye coordination is the ability of both eyes to work together as a team to provide a fused image with depth.
Vergence is the motor ability that allows us to move our eyes to point them at the target. However, binocularity comes from the the sensory ability to interpret two images into one richer image. Each eye actually sees a slightly different image. The brain puts these images together and creates a 3D picture out of it by a process called fusion. If your eyes aren’t team players, it is difficult to judge depth, relationships, and other types of spatial awareness.
If your eyes are not aligned well, your brain has a hard time fusing the two images, which can lead to double vision, confusion or ignoring an image (suppression).
Think of a pair of binoculars. If you don’t have the two oculars set up correctly, it doesn’t feel good and it is hard to concentrate on what you are looking at, or judge where you are looking. When this happens, many people will ignore one eye and just use the other. The brain makes these types of compensations as well.
Depth perception is the visual ability to perceive the world in three dimensions, (width, height, and depth). This 3D perception, or stereopsis, is our ability to see objects in spatial dimensions when the two images of the eyes are put together.
Third degree fusion (3D), or stereopsis, allows us to see where objects are in space in relation to where we are in space accurately, like a radar system. Radar systems use two trajectories to get an “X” marks the spot on a target. If you only had one trajectory, you would have to guestimate where on that line the target was sitting. If you cross reference with another line, you can accurately tell where the object is. Similarly, when our eyes coordinate together to pinpoint an object accurately, we derive meaning of how far away it is. However, with 3D vision, you are getting a much richer and fuller image compared to the images coming in through either eye.
Eye Movement Skills – Ocular Motility
Ocular motility is how well and efficiently you move your eyes. These are motor skills that allow us to move our eyes so we can fixate on objects (fixation), to quickly and accurately jump from one object to another (saccades), and to track moving objects efficiently (pursuits). This is a skill that gives us speed and control of our eye muscles to accurately inspect our environment.
Smooth, accurate eye movements are very important when it comes to paying attention, copying from the chalkboard or book, reading efficiently, and doing well in sports. Problems in this area can lead to all sorts of problems in school if they are not detected early.
Signs & Symptoms of Visual Input Skill Problems
Efficient academic and athletic performance depends on the ability to focus the eyes rapidly and automatically, regardless of the working distance to make targets clear. Activities such as reading and writing require the ability to sustain and maintain prolonged focus up close. Copying from one place to another requires a change in accommodative focus that is rapid and efficient. Visual focus is also intimately related to the ability to sustain visual attention.
Signs / Symptoms of Focusing Difficulties
- Excessive time completing assignments
- Excessive time copying from the board
- Avoiding close work
- Blurring of print
- Eyes “hurt” or “tired”
- Reduction of comprehension when reading
- Reading slowly
- Short attention span
- Vocalizes when reading “silently”
Signs / Symptoms of Poor Eye Teaming
- Double vision
- Words moving around on a page
- Motion Sickness
- Difficulty catching/hitting a ball
- Decreased depth perception
- Inefficient eye-hand or eye-body coordination
- Short attention span for near work
- Closing or covering of one eye
- Excessive blinking
- Holding a book too close
- Poor handwriting
- Reduced reading comprehension
Signs / Symptoms of Poor Eye Movement Control
- Use of a finger or marker when reading
- Loss of place when reading, writing or copying
- Difficulty copying from the board
- Skipping or repeating words
- Head movement side to side while reading
- Difficulty in sports
Note that many medications can negatively effect the visual system. Common medications that can affect accommodation include antihistamines, Phenytoin, Ritalin and other amphetamines used for ADD, and Dexedrine.
Thanks to Dr. Mary McMains, OD, MEd, FCOVD.
At our Opto-mization™ Neurovisual Performance Centres, our aim is to provide our clients with the complete picture on the benefits neurovisual training can offer.