Visual Impairment
Because of the complexity of the visual system, a variety of visual impairments can be seen. Impairments may result from injury to cranial nerves, eyes, optic chiasm, tracts, radiations, or cortical structures (119,120).
Early after injury, a child may appear to be functionally blind. Although vision is often assessed by looking at response to visual threat and visual tracking, these responses do not differentiate between peripheral and central impairments. One must assess cranial nerve function to make that differentiation.Visual acuity reduction is the most frequently detected deficit in children, but the severity varies and is associated with severity of injury (119). Visual acuity reduction is commonly associated with frontal lobe injuries (119,120). In children with greater visual acuity impairment, optic nerve atrophy, either complete or partial, is present (119). Usually, optic atrophy is seen within 1 month after injury (120), and is correlated with the site of impact and not necessarily with the overall severity of the brain injury. Chiasmatic injury results in bitemporal visual field impairment of varying degree and is found in 0.3% of TBI cases. It may be identified on MR imaging (121).
Homonymous hemianopsia is seen with injuries to the optic tracts and is often associated with hemorrhage and hemiparesis. Prism lenses may be of assistance, as well as learning compensatory techniques to increase scanning of the full environment (122). The presence of visual field impairments may be associated with more severe neuropsychological impairments (123).
Central visual dysfunction may be described as visual processing or visual perceptual problems. Cortical injury is responsible for this type of impairment and may not be confined to the occipital lobes. For example, involvement of temporal lobes may produce visual memory impairment, and involvement of parietal lobes may produce impairment of spatial awareness (124).
Injury of the third, fourth, and sixth cranial nerves may lead to a variety of visual problems (125). Diplopia may result from extraocular muscle imbalance most commonly due to trochlear palsy (125) and may be present at all times or just in particular gazes. Patching is commonly used to eliminate diplopia but results in monocular vision and related disadvantages (126). In children under 11 years old, it is important to patch eyes in an alternating manner to avoid difficulty with amblyopia. Visual motor impairments due to unilateral abducens nerve palsy in children usually resolve spontaneously within six months (127). Deficits that persist longer than six months are more likely to be associated with bilateral or complete abducens nerve palsy and are unlikely to resolve spontaneously (127).
Difficulties with convergence may also result in diplopia, and are believed to be due to supranuclear impairment. Anatomic correlates of diplopia have not been well described (125). Accommodation may also be impaired (128).