Objective assessment of the human visual attentional state

Visual evoked potential evaluation following brain injury in school-aged children

Aim: The research aimed to establish reference values of visual evoked potentials among school-aged children after brain injury. Methods: Eighteen patients with persisting visual symptoms after brain injury have been examined. A pattern-VEP test has been used during the examination. Results: The prolongation of the N2 wave in 55,6%-66,6%, P wave in 55,7%-66,7%, and N3 wave in 16,7%-22,2% was determined in the research group. Likewise, the decrease in the amplitude of the P wave was determined in the case of 16,7%-33,3%. According to the topography, we concluded that the prechiasmatic alteration was predominantly determined as bilateral in the optic pathways, with emphasis equally on the right and left. Conclusions: VEP evaluation remains one of the most credible methods of examination. In the case of moderate or severe traumatic optic neuropathy, it allows the detection of damage to the optic pathways before the appearance of organic changes that are often irreversible. The possibility of early detection of such modifications could justify the initiation of a dosed stimulatory treatment, to avoid damage to the optic pathways that would induce secondary optic atrophy. Abbreviations: VEP = visual evoked potentials, MRI = magnetic resonance imaging.

The effect of spectral filters on VEP and alpha-wave responses

PURPOSE

Spectral filters are used to treat light sensitivity in individuals with traumatic brain injury (TBI); however, the effect of these filters on normal visual function has not been elucidated. Thus, the current study aimed to determine the effect of spectral filters on objectively-measured visual-evoked potential (VEP) and alpha-wave responses in the visually-normal population.

METHODS

The full-field (15°H×17°V), pattern-reversal VEP (20' check size, mean luminance 52cd/m(2)) was administered to 20 visually-normal individuals. They were tested with four Intuitive-Colorimeter-derived, broad-band, spectral filters (i.e., gray/neutral density, blue, yellow, and red), which produced similar luminance values for the test stimulus. The VEP N75 and P100 latencies, and VEP amplitude, were recorded. Power spectrum analysis was used to derive the respective powers at each frequency, and peak frequency, for the selected 9-11Hz components of the alpha band.

RESULTS

Both N75 and P100 latencies increased with the addition of each filter when compared to baseline. Additionally, each filter numerically reduced intra-session amplitude variability relative to baseline. There were no significant effects on either the mean VEP amplitude or alpha wave parameters.

CONCLUSIONS

The Intuitive Colorimeter filters significantly increased both N75 and P100 latencies, an effect which is primarily attributable (∼75%) to luminance, and in some cases, specific spectral effects (e.g., blue and red). VEP amplitude and alpha power were not significantly affected. These findings provide an important reference to which either amplitude or power changes in light-sensitive, younger clinical groups can be compared.

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.

Effect of oculomotor rehabilitation on accommodative responsivity in mild traumatic brain injury

Accommodative dysfunction is a common oculomotor sequelae of mild traumatic brain injury (mTBI). This study evaluated a range of dynamic (objective) and static (subjective) measures of accommodation in 12 nonstrabismic individuals with mTBI and near vision-related symptoms before and after oculomotor training (OMT) and placebo (P) training (6 wk, two sessions per week, 3 h of training each). Following OMT, the dynamics of accommodation improved markedly. Clinically, there was a significant increase in the maximum accommodative amplitude both monocularly and binocularly. In addition, the near vision symptoms reduced along with improved visual attention. None of the measures were found to change significantly following P training. These results provide evidence for a significant positive effect of the accommodatively based OMT on accommodative responsivity. Such improvement is suggestive of oculomotor learning, demonstrating considerable residual brain-visual system plasticity in the adult compromised brain.

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.

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.