Binasal Occlusion (BNO), Visual Motion Sensitivity (VMS), and the Visually-Evoked Potential (VEP) in mild Traumatic Brain Injury and Traumatic Brain Injury (mTBI/TBI).

The diagnosis and treatment of the possible visual sequelae in those with traumatic brain injury (TBI) represents an important area of health care in this special population. One of their most prevalent yet elusive visual symptoms is visual motion sensitivity (VMS). In this review, we present the basic VMS phenomenon and its related symptoms, clinical studies in the area, clinical research investigations using the visual-evoked potential (VEP) as a cortical probe, and possible mechanisms and related neurophysiology that may underlie VMS. Lastly, therapeutic interventions are briefly described, as well as future directions for clinical research and patient care in those with VMS and TBI.

A Novel Computer Oculomotor Rehabilitation (COR) Program for Mild Traumatic Brain Injury (mTBI).

Individuals with traumatic brain injury (TBI) manifest a wide range of visual dysfunctions. One of the most prevalent involves the oculomotor system, which includes version, vergence, and accommodation. However, until recently, there has been no comprehensive, computer-based program for remediation of these oculomotor deficits. We present such an oculomotor rehabilitation program that has been tested in a clinical trial in patients having TBI with a high degree of success based on before-and-after objective system recordings, performance measures, and related visual symptomotology. The basic program components include a versatile stimulus package incorporating the attentional paradigm of rapid serial visual presentation (RSVP), the ability to add a visual and/or auditory distractor to the training to increase difficulty level ("task loading"), automated assessment of RSVP errors, and automated assessment of visual performance over the training period. Program limitations and future directions are also considered.

Effect of luminance on the visually-evoked potential in visually-normal individuals and in mTBI/concussion.

PURPOSE: To assess quantitatively the effect of luminance on VEP amplitude and latency in visually-normals (VN) and patients with mild traumatic brain injury (mTBI). METHODS: VN individuals (n = 20) and those with mTBI (n = 19) participated. Those with mTBI were assessed 1-10 years post-injury (mean = 4.97 years), with the exception of one subject. Pattern VEP testing was employed using the DIOPSYS™ NOVA-TR system, with a 74 cd m-2 baseline luminance. Luminance levels were reduced with five different neutral density (ND) filters (0.5, 1.0, 1.5, 2.0 and 2.5) and compared to the baseline response. All testing was performed under binocular-viewing conditions with full refractive correction in place. RESULTS: In both groups, mean VEP amplitude reduced with decrease in luminance (p < 0.05). At each luminance level, the mean VEP amplitude was significantly lower in mTBI than in the VN population (p < 0.05). In both groups, the mean VEP latency increased progressively with reduction in luminance (p < 0.05), with it being significantly higher in mTBI than in the VN population (p < 0.05). CONCLUSIONS: High luminance levels produced an optimal VEP response in both populations. VEP amplitude was robust, whereas latency progressively increased in both groups as luminance decreased. The latency increase with decreased luminance was significantly larger in those with mTBI, thus suggesting that latency can be used to differentiate reliably between VN individuals and those with mTBI.

Objective assessment of visual attention in mild traumatic brain injury (mTBI) using visual-evoked potentials (VEP).

PURPOSE: To quantify visual attention objectively using the visual-evoked potential (VEP) in those having mild traumatic brain injury (mTBI) with and without a self-reported attentional deficit. RESEARCH DESIGN AND METHODS: Subjects were comprised of 16 adults with mTBI: 11 with an attentional deficit and five without. Three test conditions were used to assess the visual attentional state to quantify objectively the VEP alpha band attenuation ratio (AR) related to attention: (1) pattern VEP; (2) eyes-closed; and (3) eyes-closed number counting. The AR was calculated for both the individual and combined alpha frequencies (8-13 Hz). The objective results were compared to two subjective tests of visual and general attention (i.e. the VSAT and ASRS, respectively). RESULTS: The AR for both the individual and combined alpha frequencies was found to be abnormal in those with mTBI having an attentional deficit. In contrast, the AR was normal in those with mTBI but without an attentional deficit. The AR correlated with the ASRS, but not with the VSAT, test scores. CONCLUSIONS: The objective and subjective tests were able to differentiate between those having mTBI with and without an attentional deficit. The proposed VEP protocol can be used in the clinic to detect and assess objectively and reliably a visual attentional deficit in the mTBI population.

Proposed objective visual system biomarkers for mild traumatic brain injury.

The challenge and search for objectively based biomarkers to assess for the presence of concussion/mild traumatic brain injury is a high priority for the military establishment. We present a documented overview of specific test areas and related targeted, high-yield, objectively based parameters that may be potential "vision biomarkers" for the detection of concussion/mild traumatic brain injury based on results from our laboratory and others, with emphasis on oculomotor aspects. These findings have military relevance with respect to the initial diagnosis in the battlefield and in the far-forward medical facilities, pre-/postdeployment issues, pre-/postvisual rehabilitation evaluation, fitness-for-duty assessment, and establishment of a return-to-duty timeline.

Effect of binasal occlusion (BNO) and base-in prisms on the visual-evoked potential (VEP) in mild traumatic brain injury (mTBI).

PURPOSE: To assess quantitatively the effect and relative contribution of binasal occlusion (BNO) and base-in prisms (BI) on visually-evoked potential (VEP) responsivity in persons with mild traumatic brain injury (mTBI) and the symptom of visual motion sensitivity (VMS), as well as in visually-normal (VN) individuals. RESEARCH DESIGN AND METHODS: Subjects were comprised of 20 VN adults and 15 adults with mTBI and VMS. There were four test conditions: (1) conventional pattern VEP, which served as the baseline comparison condition; (2) VEP with BNO alone; (3) VEP with 2 pd BI prisms before each eye; and (4) VEP with the above BNO and BI prism combination. RESULTS: In mTBI, the mean VEP amplitude increased significantly in nearly all subjects (∼90%) with BNO alone. In contrast, in VN, it decreased significantly with BNO alone in all subjects (100%), as compared to the other test conditions. These objective findings were consistent with improvements in visual impressions and sensorimotor tasks in the group with mTBI. Latency remained within normal limits under all test conditions in both groups. CONCLUSIONS: Only the BNO condition demonstrated significant, but opposite and consistent, directional effects on the VEP amplitude in both groups. The BNO-VEP test condition may be used clinically for the objectively-based, differential diagnosis of persons suspected of having mTBI and VMS from the VNs.

Effect of oculomotor vision rehabilitation on the visual-evoked potential and visual attention in mild traumatic brain injury.

PRIMARY OBJECTIVE: The purpose of the experiment was to investigate the effect of oculomotor vision rehabilitation (OVR) on the visual-evoked potential (VEP) and visual attention in the mTBI population. RESEARCH DESIGN AND METHODS: Subjects (n = 7) were adults with a history of mild traumatic brain injury (mTBI). Each received 9 hours of OVR over a 6-week period. The effects of OVR on VEP amplitude and latency, the attention-related alpha band (8-13 Hz) power (µV(2)) and the clinical Visual Search and Attention Test (VSAT) were assessed before and after the OVR. RESULTS: After the OVR, the VEP amplitude increased and its variability decreased. There was no change in VEP latency, which was normal. Alpha band power increased, as did the VSAT score, following the OVR. CONCLUSIONS: The significant changes in most test parameters suggest that OVR affects the visual system at early visuo-cortical levels, as well as other pathways which are involved in visual attention.

Optimization of the pattern visual evoked potential (VEP) in the visually-normal and mild traumatic brain injury (mTBI) populations.

PRIMARY OBJECTIVE: The purpose of this study was to assess the effect of check size (CS) and contrast (C) on VEP amplitude and latency in visually-normal (VN) and in mild traumatic brain injury (mTBI) adults to develop an optimized test protocol in each group. RESEARCH DESIGN AND METHODS: Subjects were comprised of VN (n = 19) and individuals with mTBI (n = 16). Full-field, pattern VEP testing was employed with three different CSs (10, 20 and 40 min arc) and at two C levels (20 and 85%). RESULTS: There was a significant effect of CS and C on the VEP amplitude and latency in both groups. The 20 min arc CS at both contrast levels produced the largest VEP amplitude, in conjunction with normative latency values, in both populations. There was a significant differential effect of CS and C on VEP responses in the visually symptomatic vs. asymptomatic mTBI sub-groups. A significant correlation was found between time since their most recent brain injury and VEP amplitude for the 20 min arc CS at low contrast. CONCLUSIONS: Use of the 20 min arc CS at both contrast levels represents an optimized clinical VEP test protocol in both the VN and mTBI groups. This protocol is rapid, high yield, and targeted for each diagnostic group.

The effect of retinal defocus on simple eye-hand and eye-foot reaction time in traumatic brain injury (TBI).

PRIMARY OBJECTIVE: The purpose of the experiment was to assess the effect of retinal defocus on simple eye-hand (E-H) and eye-foot (E-F) reaction time (RT) in traumatic brain injury (TBI). DESIGN AND METHODS: Sixteen subjects with traumatic brain injury (five males and 11 females; aged 22-34 years) participated in the experiment. These were compared with 16 visually-normal, age/gender-match subjects. Retinal defocus was introduced optically (plano, +1, +2, +3, +4, +10D and +2D × 90) in the spectacle plane with binocular viewing. E-H and E-F RT were assessed binocularly using the RT-2S Simple Reaction Time Tester (Advanced Therapy Products, Glen Allen, VA). The test target colour and angular subtense simulated a conventional red/green traffic signal at 120 feet. RESULTS: There was no significant effect (p > 0.05) of retinal defocus on either E-H or E-F RT in each population. There was a significant effect (p < 0.05) of TBI on both E-H and E-F RT as compared with the normative data, with it being longer and more variable in TBI. Each RT condition was longest in those with moderate TBI. CONCLUSIONS: Both RTs were robust to retinal defocus, thus suggesting central nervous system insensitivity for this simple RT task. However, the increased RTs and related variability found in TBI, especially in moderate TBI, have potential safety implications (e.g. driving a car, ambulating).

Effect of binasal occlusion (BNO) on the visual-evoked potential (VEP) in mild traumatic brain injury (mTBI).

PRIMARY OBJECTIVE: The purpose of the experiment was to assess the effect of binasal occlusion (BNO) on the visually-evoked potential (VEP) in visually-normal (VN) individuals and in those with mild traumatic brain injury (mTBI) for whom BNO frequently reduces their primary symptoms related to abnormally-increased visual motion sensitivity (VMS). DESIGN AND METHODS: Subjects were comprised of asymptomatic VN adults (n = 10) and individuals with mTBI (n = 10) having the symptom of VMS. Conventional full-field VEP testing was employed under two conditions: without BNO and with opaque BNO which blocked regions on either side of the VEP test stimulus. Subjective impressions were also assessed. RESULTS: In VN, the mean VEP amplitude decreased significantly with BNO in all subjects. In contrast, in mTBI, the mean VEP amplitude increased significantly with BNO in all subjects. Latency was normal and unaffected in all cases. Repeat VEP testing in three subjects from each group revealed similar test-re-test findings. Visuomotor activities improved, with reduced symptoms, with BNO in the mTBI group. CONCLUSIONS: It is speculated that individuals with mTBI habitually attempt to suppress visual information in the near retinal periphery to reduce their abnormal VMS, with addition of the BNO negating the suppressive influence and thus producing a widespread disinhibition effect and resultant increase in VEP amplitude.

Objective assessment of the human visual attentional state.

PRIMARY OBJECTIVE: The purpose of this study was to develop an objective way to assess human visual attention using the alpha-band component of the visual-evoked potential (VEP). DESIGN AND METHODS: Six different attentional conditions were tested: eyes-open, eyes-closed, eyes-closed with backwards number counting, and three rapid-serial visual presentation (RSVP) tasks. Eighteen visually normal, young-adult subjects (ages 21-28 years) were tested binocularly at 1 m for each condition on two separate days. The Diopsys™ NOVA-TR system was used to obtain the visual-evoked potential (VEP) and extracted alpha wave and its related power spectrum. Additionally, the Visual Search and Attention Test (VSAT) was administered as a subjective measure of visual attention. RESULTS: Subjects exhibited significant decreases in power in the alpha band when comparing the eyes-closed with the eyes-open conditions, with power in the eyes-closed condition being, on average, twice as large. The response from the other four conditions did not reflect the differential attentional demands. The ratio of the power in the eyes-closed condition to the eyes-open condition in the lower-alpha frequencies (8-10 Hz) was found to be significantly correlated with the group's performance on the VSAT, especially the 10-Hz component. CONCLUSIONS: An individual's ability to attenuate their alpha component during visual processing may be a predictor of their visual attentional state. These findings solidify the role of the VEP alpha subcomponent as an objective electrophysiological correlate of visual attention, which may be useful in the diagnosis and treatment of human visual attention disorders in the future.

Effect of test duration on the visual-evoked potential (VEP) and alpha-wave responses.

PRIMARY OBJECTIVE: The purpose of this study was to assess the effect of test duration on the visual-evoked potential (VEP) and related alpha power spectrum measures. DESIGN AND METHODS: Two conditions (eyes-closed and eyes-open) were tested using four different durations: 10, 20, 45, and 60 s. The Diopsys™ NOVA-TR system was used to obtain the visual-evoked potential (VEP) and extracted alpha wave with its related power spectrum. Sixteen visually normal, young-adult subjects (aged 22-25 years) participated in the experiment. The stimulus for the eyes-open condition consisted of a black-and-white, alternating checkerboard pattern with a small central fixation target. All trials were performed during one session. RESULTS: Regarding the VEP parameters, only variability of the VEP amplitude changed significantly with test duration. Sentence should end with a period, not a colon. It decreased with increasing test duration, with the 45- and 60-s trials showing similarly low variability. Regarding the alpha-wave parameters, test duration did not have a significant effect on either the mean alpha power or its variability across trials. CONCLUSIONS: The findings demonstrate that forty-five-second test durations are sufficient to minimize intra-session variability of the VEP amplitude and latency measurements, whereas 10-s test durations may be sufficient for accurate measurement of the alpha wave. Optimization of test duration allows for repeatable measures with less total test time. This is especially important for special clinical populations.

Distance perception in mild traumatic brain injury (mTBI).

BACKGROUND: The purpose of this study was to assess monocular and binocular distance perception, and stereoacuity, in individuals with mild traumatic brain injury (mTBI) who reported the symptom of "poor depth perception"; METHODS: Ten patients with mTBI were tested and compared with ten visually-normal asymptomatic individuals in the following areas: perceived distance, stereoacuity at distance (3 meters) and near (40 cm), and a 9-item 5-point rating-scale questionnaire related to distance perception. Distance perception was assessed under monocular and binocular viewing conditions in both clustered and isolated static environments. Magnitude estimation was used to obtain the distance perception response function of physical versus perceived distance using common objects positioned at distances of 0.77 to 12.84 meters. RESULTS: The mean distance perception response function slopes were not significantly different in the two groups for any of the test conditions. Stereoacuity (sec arc) was slightly reduced at both near and distance in the individuals with mTBI (36 ± 24.58 and 84 ± 68.34, respectively) as compared with the normal subjects (20 ± 0 and 51 ± 9.93, respectively). The mTBI group mean symptom score was 3.24 ± 0.26 indicating a moderate problematic level; CONCLUSIONS: Similarity of the mean distance response functions in the mTBI group under monocular and binocular viewing conditions suggested that their misperception of distance was not due to a "binocular vergence" problem. Similarly, the slightly reduced stereoacuity in the mTBI group was not sufficient to explain their symptom of "poor depth perception." Thus, it is speculated that this problem reflects a higher-level cortical perceptual phenomenon related to diffuse brain damage in areas dealing with visuo-spatial mapping.

Effect of different stimulus configurations on the visual evoked potential (VEP).

The purpose of this study was to assess changes in the response profile of the pattern visual evoked potential (VEP) using three stimulus configurations simulating visual-field scotomas: central circular and central blank fields increasing incrementally in diameter from 1° to 15°, hemi-field, and quadrant patterns. Five visually normal adult subjects (ages 22-68 years) were tested binocularly at 1 m for each stimulus configuration on 5 separate days. A checkerboard test pattern (64 × 64 black-and-white checks, 85% contrast, 64 cd/m(2) luminance, 20 s of stimulus duration, 2-Hz temporal frequency) was used. The group mean VEP amplitude increased in a linear manner with increase in the central circular diameter (y = 0.805x + 2.00; r = 0.986) and decrease in central blank field diameter (y = -0.769x + 16.22; r = 0.987). There was no significant change in latency in nearly all cases. The group mean coefficient of variability results indicated that the VEP amplitude was repeatable for the different stimulus configurations. The finding of VEP response linearity for the circular stimulus fields, and repeatability for all stimulus configurations, suggests that the clinician may be able to use the VEP technique with the suggested test patterns as a rapid and simple tool for objective assessment for several types of visual-field defects for a range of abnormal visual conditions and special populations.

Effects of sweep VEP parameters on visual acuity and contrast thresholds in children and adults.

BACKGROUND: There are many parameters that may impact the thresholds obtained with sweep visually evoked potentials (sVEP), yet a number of these parameters have not been systematically studied, and there is no recognised standard for sVEP recording. In this study, the effects of electrode placement, temporal frequency, sweep direction, presence of a fixation target, stimulus area, and sweep duration on visual acuity (VA) and contrast thresholds of the sVEP were investigated. Additionally, the effect of these parameters on the number of viable threshold readings obtained from five active electrodes was investigated. METHODS: Participants were six children (aged 6-8 years) and six adults (aged 17-30 years) with normal vision. Binocular sVEP VA and contrast thresholds were measured for two electrode placements (ISCEV and PowerDiva) of five active electrodes, three temporal frequencies (6, 7.5, and 10 Hz), two sweep directions (low to high and high to low), presence or absence of a fixation target, three stimulus areas, and three sweep durations. RESULTS: There were differences between adults and children with respect to visual acuity, the adults having better VA than the children (p = 0.033 in experiment 2). Overall, there were more viable readings at 7.5 Hz than at either 10 or 6 Hz (p = 0.0014 for VA and 0.001 for contrast thresholds). The adults performed better (in terms of viable readings) with the fixation target than without it (p = 0.04). The smallest stimulus size used gave rise to fewer viable readings in both adults and children (p = 0.022 for VA and 0.0001 for contrast thresholds). The other parameters (electrode placement, sweep direction and sweep duration) did not give rise to significant differences. CONCLUSIONS: A temporal frequency of 7.5 Hz, a stimulus area of 4° or larger for VA and 10° or larger for contrast thresholds, and the use of a fixation target gave more viable readings, and may be indicated for future application. Consideration of the number of viable readings showed more differences between parameters than the actual thresholds, and it is suggested that more readings presumably would yield more reliable threshold measurements.