Objective assessment of visual dysfunction in the acquired brain injury (ABI) population using the visual-evoked potential (VEP)

Abstract

Purpose: To assess quantitatively and objectively selected visual dysfunctions in patients with mild traumatic brain injury (mTBI) (i.e., increased abnormal visual motion sensitivity (VMS), attentional deficits) and stroke (i.e., hemianopic visual field defects) by using empirically-derived, optimized pattern visual evoked potential (VEP) parameters derived from our laboratory. Furthermore, the goal was to develop simple and reliable clinical VEP protocols to assess the aforementioned visual dysfunctions in acquired brain injury.

Methods: Four experiments were performed binocularly with full refractive correction using an objective, pattern VEP technique. Experiments #1-3 included both visually-normal (VN) adults and adults with mTBI, all ages 18-70 years. Experiment #4 included adult patients with stroke and hemianopic visual field defects, all ages 18-70 years. The following tests and stimulus conditions were used in Experiments #1-4: Experiment #1 – central field VEP with 10, 20, and 40 min arc check sizes at low (20%) and high (85%) contrast levels; Experiment #2 – central field VEP (baseline), binasal occlusion only (BNO), base-in prism (BI) only (4 pd total), and BNO with 4 pd BI; Experiment #3 – central field VEP (eyes open (EO), baseline), eyes-closed (EC, “relaxed”), and eyes-closed number counting (ECNC, “increased attentional state”); Experiment #4 – central field VEP, intact hemi-field only, and hemianopic field only.

Results: The followings results were found: Experiment #1 – The 20 min arc check size provided the largest VEP amplitude and normative latency values at both contrast levels in both the VN and mTBI groups. These optimal parameters were then used to measure VEP responses in Experiments #2-4. Experiment #2 – With BNO alone, the VEP amplitude was larger in individuals with mTBI (90%) and smaller in the VN (100%) groups, as compared to other two test conditions and baseline. In addition, with BNO only, those with mTBI demonstrated improvement in their visual impressions and in performing specific sensorimotor tasks. Experiment #3 – Objectively-based alpha attenuation ratio (AR = EC ÷ EO, ECNC ÷ EC) was able to detect, assess, and differentiate between mTBI with versus without an attentional deficits, as well as between VNs. These objective AR findings were correlated with the subjective Adult ADHD Self-Report Scale (ASRS) questionnaire scores. Experiment #4 – The group and individual VEP findings showed that the central field and the intact hemi-field VEP amplitudes were larger than found in the hemianopic field. Moreover, these objective findings were correlated with the subjective clinical perimetric results. Conclusions: The optimized VEP parameters provided quantitative, rapid, reliable, and repeatable responsivity in all experiments. These findings demonstrated that the conventional pattern VEP could be beneficial for researchers in general, as well as clinicians to differentiate between mTBI versus the VN group with a high probability, and also between mTBI with versus without an attentional deficit. In addition, the VEP could be used clinically to detect and assess hemianopic visual field defects in patients with stroke. Based on these findings, the VEP has the potential to be used as an objective visual system biomarker for the diagnosis of mTBI/concussion, and also as an objective adjunct clinical tool to detect visual field defects in patients with stroke.