Concussion Vision Issues

Concussion Vision Issues – Overview

Concussion vision issues affect a large number of patients. This leads to an inability for patients to comfortably carry out many activities of daily life (e.g. reading). Following an mTBI, it is theorized that the integration of vision subsystems, focal and ambient, break down. Full concussion vision evaluation should include: basic optometric considerations, as well as oculomotor & non-oculomotor functional testing. Repetitive vision exercises, +/- aids, are believed to accelerate & enhance the natural neuroplastic recovery.

Concussion Vision Issues – More in-depth

The first part of this Bits and Bytes article on concussions and vision will look at the frequency and type of problems that individuals with concussions (mTBI) encounter. It will also very briefly summarize the vision theory regarding deficits and the frequently employed treatment approaches. The second part will look at the evidence for vision treatment, dosages & who should provide them.

Concussion Vision Issues – Frequency

The frequency of TBI in the population is estimated to be 150-300 per 100,000 individuals.¹ It has been estimated that 70-80 % of these TBIs are mild TBI. A retrospective study done on TBI outpatients reported that 90 % of the 160 individuals surveyed had oculomotor deficits.² Taken together, these statistics mean that, at any one time, a large number of individuals are recovering from concussions, and an overwhelming majority of these individuals are dealing with vision problems.  Vision problems in patients with concussion / PCS contribute to symptoms such as headaches and fatigue. They result in dysfunction, e.g. poor concentration, reduced ability or inability to read, drive, study and / or work. These in turn lead to substantial reduction in the concussed person’s quality of life, and a huge productivity loss & cost to their societies.

Concussion Vision Issues – Theory

Much of the theory about vision therapies and treatment originated from the work Dr. W. Padula.³ He proposed (based on his own research, clinical experience and earlier primate studies done by other authors), that vision is bimodal.  The first mode is the “focal.” It is the slower acting of the two modes, and is content driven. In other words, it is primarily involved in identifying what is being looked at. The second mode, the “ambient,” works much faster. It is context driven and has its origins in survival. It is primarily focused on what is around the thing being viewed, and its potential threat. The ambient system manages the oculomotor functions of the eye. For example, how to efficiently and seamlessly move the eyes between targets (i.e. saccades). The ambient visual system is also highly integrated with the vestibular and somatosensory system to maintain posture and assist locomotion. A good example of the two systems working together is the high level vision task of walking while reading a book. The focal system is concerned with the content of the book. The ambient manages the movement of the eyes from word to word, the maintenance of upright posture, and the avoidance of obstacles. Usually these two systems, focal and ambient, work like hand in glove. However in brain injury (e.g. mTBI) this integration is thought by neuro-optometrists to break down. Most often the breakdown occurs in the ambient system causing focalization.

Vision has many levels from its basic retinal processing, through subcortical and subconscious cortical sensory matching, up to conscious visual cognition.⁴ For any given level to work, the lower more basic capacities need to function well. It is believed that the clinician best assists the individual to recover visual function by identifying and remediating the impairments present at the very basic levels, well below consciousness. 

Concussion Vision Issues – Assessment

Ciuffreda & Ludlam break concussion vision assessment, associated dysfunction(s) and treatments into 3 tiers.⁴ For the purposes of brevity, their model is simplified as follows:

Tier 1  Basic Optometric Assessments.

• Refractive status: the ability of the eyes to correctly bend incoming light onto the proper part of the retina.
• Binocular status: the basic ability of the brain to combined the images of the left and right eyes into one clear image.
• Health status: the assessment of the health of the eyes and their associated structures (e.g. retina, optic nerve, etc.). 

Tier 2  Oculomotor-Based Vision Assessment

• Version: the ability of the eyes to move together in the same direction (e.g. up, down, left & right). This can be further broken down into a number of motor skills of the eyes. These need to be assessed at different directions & distances.
  • Fixation: the ability to keep the eyes locked onto a single target.
  • Saccades: the ability to quickly and accurately move the eyes together between two targets.
  • Pursuit: the ability to smoothly move the eyes tracking a moving target.
• Vergence: the ability of the eyes to move in opposite directions in order to facilitate binocular vision. Like version, this can be broken down into different motor skills of the eyes:
  • Convergence: the ability to rotate the eyes inwards for viewing a near object.
  • Divergence: the ability to rotate the eyes outwards for viewing a far object.

Tier 3  Non-Oculomotor-Based Vision Assessment

• Mid-line shift: the abnormal sense of straight ahead. This is observed mostly in moderate ABI, but sometimes in mTBI patients. The shift can occur to the right, left posterior and or anteriorly. It results in postural problems, difficulty walking, and the person mistaking where they are versus other objects in the environment (e.g. bumping into furniture).
• Photosensitivity: the intolerance to light, particularly strong light (e.g. bright sunlight) or flickering lights (e.g. fluorescent and some LEDs).
• Motion sensitivity: the intolerance to dynamic and or moving environments (e.g. the supermarket effect).
• Vestibular dysfunction: the inability to keep one’s eyes stable as the person moves in their environment. This is due to problems with the inner ears’ vestibular system or by the brain’s processing of the vestibule-ocular reflex and, to a lesser degree, the neck’s cervico-ocular reflex.
• Visual field deficits: caused by damage to the retina or optic nerve or brain pathways.
• Visual processing and perceptual deficits: manifesting as figure-ground disturbances, sensory integration & delay issues.

Zelinsky notes that many vision professionals, finding no issues with a concussed individual’s structural and neurological vision systems (Tier 1), erroneously conclude there is no abnormality elsewhere in their vision system (i.e. functionally).⁵ 

Concussion Vision – Treatment

Vision therapy relies on the brain’s innate ability to observe patterns and correct its own deficits through neuroplastic change. To facilitate neuroplastic recovery, the patient is given progressively harder vision exercises, +/- temporary visual aids such as prism glasses, bi-nasal occlusion (BNO) & tints. Prisms are used for version and abnormal spatial localization (i.e. midline shift). Binasal occlusion & tints are used to lessen the motion sensitivity, often demonstrated while walking. Tints are employed for photosensitivity

References

1. Editorial: The changing landscape of traumatic brain injury. The Lancet Neurology 2012 Aug; 11 (8): 651.
2. Ciuffreda K. et al. Occurrence of oculomotor dysfunctions in acquired brain injury: a retrospective analysis. Optometry 2007 Apr; 78(4):155-61.
3. Padula, W. & Argyris, S. Post trauma vision syndrome & visual midline shift syndrome. Neurorehabilitation 1996 (6) 165-171.
4. Ciuffreda, K. & Ludlam, D. Conceptual model of optometric vision care in mild traumatic brain injury. Journal of Behavioural Optometry 2011 22 (1).
5. Zelinsky, D. Neuro-optometric diagnosis, treatment and rehabilitation following traumatic brain injuries: a brief overview.  Physical Medicine and Rehabilitation Clinics of North America 2007 (18) Pages 87-107.