Many people have heard the term post-concussion syndrome, but what is post-concussion vision syndrome? Like post-concussion syndrome, post-concussion vision syndrome is diagnosed when symptoms following a head injury persist for longer than one or two months, however is specific to symptoms related to vision.
The terms post-concussion vision syndrome (PCVS) and post-traumatic vision syndrome (PTVS) are often found in literature, and some use the terms interchangeably even though there is a distinction between the two. PTVS is an umbrella term used to include visual symptoms after any neurological impact, such as stroke, tumor, whiplash, and concussion, whereas the term PCVS is specific to concussions only.
To understand PCVS, one has to understand the visual system.
The visual system is composed of 2 separate processes that must work in harmony:
1. Focal process:
The focal process is neurologically related to our central vision, which is represented primarily by an area in our retina called the macula. When we think of “20/20” vision, it is this process we are thinking about. The focal process helps us identify objects using shape, color, size, and other visual details as cues. Our peripheral vision can also be used to identify objects, however we know that this is much more difficult to do than to directly look at an object for identification.
2. Ambient process:
The ambient process is neurologically related to our peripheral vision, which is represented by the rest of our retina outside of the macula. We use our peripheral vision to inform us where we are in space and to provide general information needed for balance, movement, coordination, and posture.
The information from this system is sent to the level of the midbrain, where it must match information from other systems before the information is fed forward to higher cortical areas. These systems include: somatosensory and vestibular system.
These matters were discussed elsewhere in our article VVM.
In addition to these two very important processes, an efficient visual system must be able to demonstrate accurate visual skills:
This is often referred to as “eye-teaming”. Our eyes are two separate organs and must learn to “team” together to look through various areas of depth, ranging from distance to near.
This is often referred to as “eye-focusing”. Like a camera lens that must change shape to focus on objects at various distances for the perfect picture, our eye has an internal lens that must act similarly. The lens is relaxed for distance viewing and must work or focus for near viewing. The lens is flexible and must be able to change shape rapidly and accurately to maintain focus appropriately on objects of various distances.
The tracking system is comprised of two visual skills:
i. Saccades are rapid eye movements that we use to change fixation between objects. These are used to jump from one word to the next when we are reading.
ii. Pursuits are slow eye movements we use to maintain focus of a slow-moving object, such as a ball being thrown through air.
More than 50% of the brain’s function is involved in vision in some way. Therefore, it isn’t surprising that any head impact can affect the visual system and result in visual symptoms.
In PCVS patients, the role the ambient visual system plays in their vision is compromised. This can lead to difficulties of knowing where we are in space, difficulty orienting in space, and can ultimately affect our balance, movement, coordination, and posture.
Visual skills, such as vergence, accommodation, and tracking, can also be affected after head injury. This can affect our ability to complete regular daily tasks including reading, computer use, driving, and taking notes to name a few. Descriptions of specific diagnoses are listed in our topics library, but here is a quick overview of some common diagnoses that can occur when the visual system is affected:
This is when the eyes have difficulty being able to converge enough to view an object at near. This can lead to symptoms of words running together or blurring when reading, double vision, headaches, falling asleep when reading, reduced reading speed, and/or reduced reading comprehension.
2. Convergence excess:
This is when the eyes converge too much when viewing an object at near. This can lead to symptoms of headache, words running together or blurring when reading, double vision, falling asleep when reading, reduced reading speed, and/or reduced reading comprehension.
This is when our eyes have difficulty controlling the internal lens system for accurate ability to focus or sustain focus normally on objects at various distances. This can lead to difficulty with blurry vision, difficulty reading, taking notes, and headaches.
4. Oculomotor dysfunction:
This is when the eyes have difficulty tracking (and includes both difficulties with saccades and pursuits). This can affect eye-hand coordination, ability to navigate through space, and reading.
5. Visual midline shift:
This is a difficult concept for most to understand. Visual midline shift, also known as abnormal egocentric localization, is one’s sense of position in space. This can lead to an inaccurate understand of where straight ahead is or where objects are in space relative to oneself. Patients may find that they are veering to one side when walking or that their visual environment, such as walls, ceilings, and floors, are tilted.
We have described this concept in detail in a previous post. Basically, the information provided by the visual system and the vestibular system in our brain does not match. Think about the analogy of the train from our previous post. VVM can often lead to symptoms of imbalance and dizziness.
The symptoms for PCVS can be experienced for many years if not treated correctly.
These can include:
- Blurred vision
- Double vision
- Difficulties with reading comprehension
- Difficulties with skipping words or lines while reading
- Words running together when reading
- Words swimming or jumping when reading
- Difficulties with changing visual focus between distance and near
- Difficulty with scrolling or using the computer and/or phone
- Difficulties with concentration
- Light sensitivity
- Motion sensitivity
- Inability to tolerate crowded or busy environments
- Poor balance
- Reduced confidence navigating through space
- Visual fatigue or eyestrain
- Difficulties with memory
Damage to the visual system cannot be seen in most cases on CT scan or MRI, nor can they be detected by standard optometric testing. A person can have 20/20 vision, yet still experience the debilitating symptoms listed above.
A thorough visual assessment should include that of standard optometric testing (visual acuity, visual prescription, and dilated eye health exam), but should also include assessment of functional visual skills (including vergence, accommodation, and tracking), spatial awareness, visual midline shift, vision-vestibular function, visual processing skills, and visual field.
Treatment can include prescribed glasses, which may contain prism, anti-fatigue lenses, tint, or partial occlusion. The content of prescribed glasses is specific to each unique case.
A visual rehabilitation program may also be recommended. Visual rehabilitation, also known as vision therapy, consists of visual activities that are designed to re-train normal visual function via active participation by the patient. For vision therapy to work effectively, the patient must be motivated, dedicated, compliant, and persistent with the activities provided.
Additionally, a patient with PCVS may also be experiencing symptoms related to other systems. Therefore, concurrent treatment with other medical professions, such as Sports Medicine Doctors, Physiotherapists, Chiropractors, and Occupational Therapists to name a few, may also be recommended.