Visual Dysfunctions

Dysfunctions of the visual system are quite common following TBI (Morton 2004). The overall incidence of cranial nerve injury in individuals hospitalized following TBI has been reported to be 19% (Bontke et al. 1993). It is a relatively new concept that the visual system can respond to treatments directed towards the visual-perceptual and/or visual motor skills in individuals with acquired neurological damage. The visual system is highly integrated with many functions other than simply sight, as it also acts as a primary sensory receptor for motor, social, cognitive, communicative, and emotive tasks. Improvements in visual-perceptual and visual-motor disorders can increase function in all the aforementioned areas and can enhance maximal functional recovery. Consequently, it is necessary to direct a fair amount of attention to visual system disorders in individuals with TBI and this aspect should be considered an essential part of any rehabilitation program (Morton 2004). In a review conducted by Riggs et al. (2007), the authors noted that visual rehabilitation studies has primarily involved stroke patients and has largely neglected the TBI population. Their review indicates that visual neglect disorders resulting from a stroke and brain injury show improvement after treatment with prisms, visuomotor feedback training and patching interventions. Moreover, a recent review by Berger et al. (2016) examined specific interventions for improving occupational performance in adults with visual impairments as a result of TBI. Results indicate that there is limited evidence to the effectiveness of vision therapy for oculomotor dysfunction, however there is sufficient evidence to support vision therapy as a means to improve visual field deficits in patients with TBI (Berger et al. 2016).

Individual Studies

Table: Incidence and Treatment of Visual Dysfunction in Individuals with Brain Injury

Discussion

Visual dysfunction post ABI can be corrected with base-in prisms, as they affect the ambient visual process by increasing the effectiveness of binocular cortical cells (Padula et al. 1994). Base-in prisms and bi-nasal occluders incorporated within the lenses of both eyes increase the amplitude of visual-evoked potentials (Padula et al. 1994). Prismatic spectacle lenses are also effective in reducing symptoms related to vertical heterophoria and concussion, as they reduce the faulty vertical alignment signal generated by the brain injury (Doble et al. 2010).

Individuals with optic nerve or post-chiasmic injury associated with ABI who complete computer-based Visual restitution training (VRT) experience visual field enlargement and increased light detection (Kasten et al. 1998). Detection training has shown improvements in visual detection, as well as improvements in other visual functions such as shape and color recognition (Kasten et al. 2000). Recently, Conrad et al. (2016) studied a home-based computer vergence therapy program used to improve binocular visual dysfunction after ABI. Participants underwent home-based visual vergence therapy five days a week for 12 weeks. Negative vergence, positive vergence, near point convergence and vergence facility all showed significant improvements over the 12 week intervention period (Conrad et al. 2016). 

When the reading dysfunction post-ABI is a result of sensory-based hemifield deficits or neuromotor deficits, saccadic occulomotor rehabilitation can lead to improvements in eye movements which are required for accurate reading (Ciuffreda et al. 2006). Repetitive occulomotor conditioning reduces the cognitive and attentional load of reading and results in a structural and systematic approach to reading. The benefits of occulomotor rehabilitation were observed in other activities of daily living such as concentration and visual scanning. Most importantly, reducing visual deficits in patients post TBI may facilitate their involvement in other therapies and contribute to overall recovery (Ciuffreda et al. 2006). 

Conclusion

There is Level 1b evidence to suggest the computer based restitution training is effective in improving the vision of those who sustain a TBI.

There is Level 4 evidence showing that base-in prisms and bi-nasal occluders are effective in treating ambient vision disturbances resulting from an ABI.

There is Level 4 evidence that prismatic spectacle lenses are effective in reducing symptom burden in patients with vertical heterophoria and post-concussive symptoms post injury.

There is Level 4 evidence that rehabilitation programs directed at improving visual function improves functional outcomes such as reading in patients post ABI.

 

Computer based restitution training has been shown to improve the vision of those who sustain a TBI.

Base-in prisms and bi-nasal occluders have been shown to be effective in treating ambient vision disturbances.

Rehabilitation programs directed at improving visual function may improve visual functional outcomes post ABI.