Reading is an incredibly complex skill. Comprehension of written material is a result of coordinated eye movements, recognition of letter, numbers, or forms, and memory retrieval of existing facts, logic, vocabulary, and much more.

Eye movements important for reading include:

  1. Fixation – The ability to keep the visual image still despite body and head movements. Our bodies are rarely completely still. The act of fixation requires input from our vestibular system, our sense of body position, and our visual system.
  2. Pursuits – The ability to smoothly track a moving object. For example, for readers who read following their pointer finger.
  3. Saccades – The ability to jump from one target to another. This requires a shift to our attention as well.
  4. Eye teaming – the ability for both our eyes to turn inward, or converge, when looking at material at near and then turn outward, or diverge, when looking at a distance.
Our focusing system, much like the zoom function used to focus a camera, also has relax or engage the proper amounts to clear reading material held at various distances. This system naturally weakens in a process known as presbyopia when we reach the ages of late 30’s and 40’s resulting in the need of ‘reading glasses’.

Attributes of visual skills that are also important to reading include:

  1. Precision – This is a measure of how accurate our eye movements are to a point of interest much like how close to a bull’s eye we can aim. If we are aiming for the 4th word a sentence and our eyes instead end up on the 6th, we would have to backtrack and would lose precious time.
  2. Control – This is seen in the stamina and flexibility of a particular visual skill. I often see patients who can voluntary converge at near point successfully on the first try, but are unable to sustain the skill when they are tired or cannot diverge quick enough to avoid blur when rapidly changing their visual attention to look at a distant object. This is the most common deficiency I see in my stroke and concussion patients. Vision rehabilitation therapy helps patients practice certain visual skills in a particular environment and regain control.
  3. Field Span and Awareness – This is a measure of how much information one is able to take in at one glance. Avid readers can remember several words from glancing at the page a single time. Field awareness refers to our peripheral awareness which is important in orientation since this system gives us reference to direct where our visual attention should go next. This is the reason why often patients who have field loss from strokes or blurry spots from diabetic eye disease or macular degeneration lose track of the sentence they are reading.
Given the complexity of this skill, it is no wonder that brain injuries due to stroke or concussions, and various eye diseases or even poor attention result in reading difficulties. Stay tuned for Visual Perception: the Challenges of Reading – Part 2.