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VISUAL PROCESSING

Ocular Motor skills are the foundation in which we build visual perceptual skills. Visual processing and ocular motor skills are often used interchangeably but are not necessarily the same.

Visual Processing is how our brain makes sense of the visual information given.

Ocular Motor skills are the base of visual processing. These skills include smooth pursuits, saccades and fixations:

  • Smooth Pursuits: Visual tracking is a visual processing skill that occurs when the eyes focus on an object as it moves across the field of vision. Visual tracking occurs with movement of the eyes to follow a moving object and not movement of the head. The eyes can track an object in the vertical and horizontal, diagonal, and circular planes. There should also be an ability to track across the midline of the eyes and with smooth pursuit of the object. 

  • Saccadic movement, or more commonly known as saccades: is the ability of the eyes to move in synchrony from point A to point B rapidly WITHOUT deviating from the path. Typically, we look for these patterns to be established in left/right and top/bottom patterns as they are the easiest to identify. However, if the saccadic movement is not impaired, the eyes should be able to move in all directions in synchrony between two or more given points. 

  • Fixations: The ability to visually attend to a target or object. Visual fixation occurs while maintaining focus on the object and typically occurs at a variety of distances and locations within the visual field. This is a skill that typically develops at about 4 weeks of age.

So many times, we may see kids who struggle with tasks like reading, writing, coordination, or other areas and miss the visual part of the difficulty. The ability to process visual information plays an important part in everything we do. The areas below are signs that a visual tracking problem may present, and visual tracking skills should be assessed.

 

  • Incoordination when visual perceptual skills or visual motor skills are required

  • Difficulty with eye-hand or general coordination

  • Difficulty with sports including those that use a ball or target

  • History of delayed developmental milestones

  • Reverse letters or numbers when writing

  • Misjudges distances or heights related to orientation of the body or body parts in movement or activities

  • Difficulty following an object across their field of vision, especially when the object crosses midline

  • Difficulty reading

  • Difficulty writing

  • Trouble copying work from one place to a paper in single plane or multi-plane locations

  • Difficulty keeping up with peers

  • Difficulty managing body on uneven surfaces, including navigaing and managing bleachers, steps, or walkways

  • Difficulty drawing or coloring

  • Trouble shifting gaze in all planes

  • Skips words or a line of words when reading or re-reads lines of text

  • Must use finger to keep place when reading

  • Poor reading comprehension

  • Short attention span

  • Difficulty comprehending or remembering what is read

  • Confusion with interpreting or following written directions

  • Writing on a slant, up or down hill, spacing letters and words irregularly

  • Confusion with left/right directions

  • Errors when copying from a chalkboard or book to paper

  • Misalignment of horizontal and vertical series’ of numbers in math problems

As we develop the base of ocular motor skill listed above we build into binocular skills. These ocular motor skills require both eyes to work together and for the brain to interpret and process the visual information.

Visual Convergence: of the eyes occurs when the two eyes need to focus on a close object, such as a book, computer, tablet, smartphone, etc.

Convergence insufficiency means the eyes struggle to focus easily for near tasks, affecting school work, attention and office performance in adults. A proper diagnosis of CI can prevent a child from being labelled as “lazy,” “spacey,” “clumsy”, “anxious,” and even misdiagnosed with ADHDdyslexia, or mild autism.

 

CI affects up to 1 in every 8 children, that is 13% of all school-aged students. It is therefore possible, that four children in every classroom may be struggling with this condition!

What are the symptoms of CI?

There are many different symptoms that can develop as a result of CI— these are the most common:

  • Eyestrain

  • Headaches or muscle tension

  • Blurred or double vision

  • Difficulty reading and concentrating

  • Uses finger or ruler when reading

  • Avoidance of close work

  • Poor hand-eye coordination

  • Anxiety

  • Motion sickness/dizziness

Visual Divergence: the opposite of convergence and is the ability to turn the two eyes outwards to look at a distant object.

Visual Accommodation: The ability to go between convergence/divergence is visual accommodation. This is a child’s ability to look up at the board and back down at their paper. Many times children have difficulty with depth perception when they lack binocular skills such as convergence and divergence. Depth perception is what allows us to step up a certain height and time when we see a curb. It allows us to gage distance and timing for sports. Depth perception is our end goal and reward for having good ocular motor and binocular skills.

Finally, the Vestibulo-Ocular Reflexes is a foundational skill for visual processing.

Vestibulo-Ocular Reflex: Uses information from the vestibular labyrinth of the inner ear to generate eye movements that stabilize gaze during head movements. This is how we stabilize our gaze. This how our movement system (Vestibular system) affects our eye movements through the fluid in our semicircular canals.

As you move your head left, right, up, or down, notice how your point of focus stays in focus. This is your VOR at work. For those with vestibular difficulties, an underdeveloped VOR would mean that nothing in the child’s visual focus would stay in place whenever his or her head moved. 

Looking at a child’s PRN – Post Rotary Nystagmus is how we access a child’s VOR. A PRN occurs when the body is rotated and then the rotation is stopped. If, while sitting upright in a chair that can be swiveled, the body is rapidly rotated to the right, the nystagmus during rotation has its slow component to the left. When the rotation stops, the slow component is the right. Simulation of the semicircular canals causes this type of nystagmus, and it is normal reaction. 

 

It is important to look a child’s ocular motor skills. Deficits in these areas can often be mislabeled and/or mistreated.

References:

nystagmus | Taber's Medical Dictionary (tabers.com)

Convergence Insufficiency - Optometrists.org

What is Visual Tracking? - The OT Toolbox

Eye-tracking: The Often Missed Reading Difficulty | Clonlara School (wordpress.com)

Normal Eye Tracking
Saccadic Movement
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