Up to 80% of patients with military mTBI report visual symptoms, including difficulty with reading and near work, spatial perception and light sensitivity. Problems with vision are also potential confounders for the other tests after mTBI; for example, a patient performing poorly on neuropsychological assessments with visual impairment may be incorrectly diagnosed with cognitive problems when in fact the limitation is visual.
The frequency of visual symptoms in TBI reflects the high proportion (~30%) of the cerebral cortex devoted to visual function. Eye manifestations of mTBI, assessed by objective assessment of visual structure and function, can provide objective and reproducible disease biomarkers, termed “oculomics”. TBI affecting the optic nerve results in a condition called traumatic optic neuropathy (TON). TON typically manifests with reductions in visual acuity, colour vision, pupil reactivity and visual field in the affected eye. Historic data suggests that this occurs in only 2% of patients with TBI, but more recent studies with more detailed assessment of the eyes suggests that optic nerve changes after TBI may be much more frequent. Optical coherence tomography (OCT) provides detailed structural and blood flow information in the optic nerve and retina. Other standard tests including pupil measurement and colour vision evaluations allow assessment of function to compare with the structural OCT measurements.
Classical teaching is that traumatic optic neuropathy is not manifest as structural retinal change (loss of nerve cells) until 6 weeks after injury. Case reports using OCT suggest that retinal changes are detectable as early as 1-2 weeks, but this has not been systematically characterised. Given that the earliest reported changes in retinal structure have been at 1-2 weeks after injury, we expect that initial assessment within the first 2-3 weeks after injury will have few injury-related structural retinal changes allowing comparison with this assessment as a baseline for evaluation of subsequent changes.
In addition to detailed assessment of optic nerve and retinal structure and function, many patients complain of problems focusing, which can be objectively measured by autorefraction.
Lead Researchers