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Concussion Vision Syndrome

Post Concussion Vision Syndrome( PCVS ) is diagnosed when symptoms, specifically visual in nature, persist for longer than 1 or 2 months, following a traumatic brain injury or head injury.

Let’s try to understand PCVS:

The visual system consists of two separate processes that must work together.

Focal processing center:

FocalThis is related to our Central vision, which is represented primarily by an area in our retinal called the macula.  This is what our 20/20 vision is.  The Focal processing center helps us identify shape, color, size and other acute visual details. 


Ambient processing center:

AmbientThis is related to our peripheral vision, which is the rest of our retina, outside of the macula.  We use our peripheral visual system to localize ourselves, and spatial awareness.  This helps us with balance, movement and posture.  

The information gathered is then sent to the level of the midbrain, where it must match information gathered by other systems (somatosensory, vestibular, etc) before it directed to higher cortical areas for further processing.

In addition to these important processes, we must also be able to demonstrate accurate visual skills:

  1. Vergence – the ability for both eyes to team together and focus through different ranges from far to near, and near to far
  2. Accommodation – the ability to “focus” like a camera and hold clear vision
  3. Tracking – consists of two separate visual systems:
    • Saccades – rapid eye movements that we use to change fixation between objects. These movements are used to jump from one word to the next when reading.
    • Pursuits-are eye movements we use to track and follow a moving object.

So what happens to the visual system after a concussion?

More than 50% of our brain is involved in vision in some way. It shouldn’t be a surprise, that any head injury or impact to the head can affect the visual system and result in visual symptoms. Most commonly a motor vehicle accident, stroke, or sports injury can have patients feeling unwell.

The Focal system may be compromised and affect clarity. The ambient system may be compromised and lead to difficulties with self-awareness in space, and consequently affect balance and movement.

Visual skills (vergence, accommodation and tracking) can also be affected after a head injury. This takes away our ability to carry out regular daily activities such as reading, computer use, driving, just to name a few.

Common Traumatic brain injury or concussion vision symptoms reported by individuals are:

  • Difficulty focusing/ concentrating
  • Headaches
  • Difficulties with reading or skipping words or lines when reading
  • Words running together when reading
  • Difficulty with glare off of screens
  • Difficulty scrolling on computers and/or phone
  • Difficulty with motion sensitivity
  • Visual fatigue or eyestrain
  • Difficulties shifting focus from far to near, and near to far
  • Double vision
  • Sensitivity to light or noise
  • Dry eye
  • Loss of balance
  • Leaning to one side



Vergence Inaccuracy – trouble eye teaming, leading to double vision, eyestrain, headaches, blurred visiON
Accommodative dysfunction – trouble focusing
Oculomotor dysfunction – trouble tracking
Visual Midline Shift – inaccurate understanding of where straight ahead position is
Visual Vestibular Mismatch – our visual input does not match input from our vestibular system

How do we test?

In addition to a basic eye examination (an eye glass prescription check, an eye health check), a visual functional assessment is conducted. This includes testing vergence, accommodation, tracking, spatial awareness, glare and contrast testing, visual midline assessment, vision-vestibular testing, visual processing and visual field testing. Neuroimaging such as CT scan or MRI are also typically ordered, but do not reveal a loss of visual skills.

How do we treat?

Treatment may be as simple as changing the prescription slightly or prescribing a low grade correction. Recommendations may include change in classroom placement, or positioning of the reading material etc. An additional pair of glasses ( or bifocals) may be given to cater to certain tasks. Special tints, occlusion measures, or prisms may be prescribed as well.

In cases where a tint, or prism or spectacle correction is not enough, a visual neuro-rehabilitation, aka vision therapy program may be recommended. It is common to co-manage with other professions such as your family physician, neurologist, speech therapist, physiotherapist or occupational therapist.

The period of recovery after a Traumatic brain injury or concussion can be as long as 1-2 years, but may remain incomplete.



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