N75 Amplitude Research Articles

Fluoxetine as a possible treatment for adult amblyopia: results of a double-blind, randomized, placebo-controlled trial

PurposeTo evaluate the effects of oral fluoxetine on visual acuity and visual-evoked potential (VEP) parameters in adults with amblyopia. MethodsIn this randomized clinical trial, adults (>18 years of age) with anisometropic or strabismic amblyopia were assigned randomly to a treatment (fluoxetine) group or a placebo group. Standard treatments for amblyopia (glasses prescription and patching) were prescribed for 4 months for all patients. The first group received fluoxetine (20 mg per day) and the second group received a placebo for 3 months. Visual acuity evaluation and VEP were performed before and after treatment. ResultsA total of 55 participants were included: 29 in the fluoxetine group and 26 in the placebo group. Mean age was 27.2 ± 8.6 years (18-54). The mean logMAR visual acuity of the amblyopic eye improved by 0.20 ± 0.24 (0-0.8) in the fluoxetine group (P < 0.001) and by 0.08 ± 0.15 (0-0.7) in the placebo group (P = 0.01); mean logMAR improvement was significantly higher in the fluoxetine group than in the placebo group (P = 0.04). At the end of the study, mean visual acuity of the fluoxetine group (0.36 ± 0.21 log MAR) was better than the placebo group (0.43 ± 0.35 log MAR). Among the VEP parameters, N75 amplitude did not change significantly in either group relative to baseline, but the changes were statistically significantly different between the two groups (P = 0.05); N135 latency improved from baseline in the fluoxetine group (P = 0.03). ConclusionsIn our study cohort, fluoxetine treatment for adult amblyopia resulted in greater improvement in visual acuity than placebo.

The effect of montages of transcranial alternating current stimulation on occipital responses-a sham-controlled pilot study.

Transcranial alternative current stimulation (tACS) refers to a promising non-invasive technique to improve brain functions. However, owing to various stimulation parameters in the literature, optimization of the stimulation is warranted. In this study, the authors aimed to compare the effect of tACS electrode montages on occipital responses. In three montage sessions (i.e., Oz-Cz, Oz-cheek, and sham), 10 healthy young adults participated, receiving 20-min 2-mA alpha-tACS. Pattern-reversal visual evoked potentials (VEPs) were measured before tACS (T0), immediately after (T20), and 20 min (T40) after tACS. Normalized changes in time-domain features (i.e., N75, P100 amplitudes, and P100 latency) and frequency-domain features [i.e., power spectral density in alpha (PSDα) and beta (PSDβ) bands] were evaluated. In contrast to our hypothesis, the occipital response decreased immediately (T20) after receiving the 20-min tACS in all montages in terms of P100 amplitude (p = 0.01). This reduction returned to baseline level (T0) in Oz-cheek and sham conditions but sustained in the Oz-Cz condition (T40, p = 0.03) after 20 min of tACS. The effects on N75 amplitude and P100 latency were statistically insignificant. For spectral analysis, both PSDα and PSDβ were significantly increased after tACS at T20, in which the effect sustained until T40. However, there was no differential effect by montages. There was no significant difference in the occurrence of sensations across the montages. The effectiveness of the blinding is supported by the participants' rate of guessing correctly. This study revealed an immediate inhibitory effect of tACS, regardless of the montages. This inhibitory effect sustained in the Oz-Cz montage but faded out in other montages after 20 min.

Visual evoked potential changes in pre-diabetics, type 2 diabetics and normal subjects

Introduction: Diabetes mellitus type 2 is the most common metabolic disorder and diabetic retinopathy is the leading cause of blindness. Persistent hyperglycemia leads to damage of microvasculature supplying the retina and optic pathway. Visual evoked potential is the most commonly used test to evaluate the integrity of visual pathway. The purpose of the study is to compare the visual evoked potential latency and amplitude between the pre-diabetes, diabetes and normal controls. Materials and Methods: There were three groups in the study with 23 patients in each group; pre-diabetic group, diabetic group and controls. Group was made based on fasting blood sugar levels. Pattern visual evoked potential was measured in all the groups by connecting scalp electrodes according to 10-20 International electrode placement system. Latency and amplitude of N75, P100 and N145 were measured and used for statistical analysis. Results: All the parameters individually were compared between three groups using ANOVA test. There was no statistical difference between latencies and amplitude all the three parameters N75, P100, N145 in all the three channels O1-NE, O2- NE, Oz-NE in all the three groups. Conclusion: There is no differences in the visual evoked potential latency and amplitude in the between pre-diabetics, diabetes and controls. Keywords: Visual evoked Potential, Diabetic retinopathy, Pre-diabetes, P100, N75, N145.

Evoked potentials in diagnosis of visual dysfunction in amateur boxers

ABSTRACTObjective: Injuries with varying degrees of temporary or permanent visual dysfunction are common in boxing. This study presents clinical diagnostic information regarding the functional integrity of the visual system in elite amateur boxers. The objective of this study was to assess the presence of normal or abnormal pattern visual evoked potentials (VEP). VEP in boxers were analyzed in relation to the nonathletic group and years of boxing activity.Methods: Clinical examination involved 31 boxers (21 male and 10 female) and 31 controls homogeneous in terms of age and gender. Pattern-reversal VEP elicited by checkerboard stimuli with large (LC) and small checks (SC) under monocular condition were applied. The latency and amplitude of N75, P100 and N135 components of the VEP waveform were analyzed. Absolute values and interocular differences of P100 latency and N75-P100 amplitude were used in determining VEP abnormalities.Results: Individual analysis showed prolonged P100 latency in both eyes in one male boxer. Interocular P100 latency differences beyond 8 ms were observed in three male boxers. The N75-P100 amplitude of four boxers exceeded the normal range in both eyes for the LC stimulation and one boxer for the SC stimulation. Interocular N75-P100 amplitude differences beyond the normal range in two cases for both the LC and the SC stimulation were confirmed. There was a positive correlation between years of boxing activity and N75 latency in SC (R = 0.480, p < 0.05) and N75-P100 amplitude in LC (R = -0.370, p < 0.05).Conclusion: Long-term boxing training may cause impairments in neural conductivity in the visual pathway. VEP seem to be a valuable tool in the neurophysiological diagnosis of visual function in contact sports. They can be recommended as a systematical examination for boxers during training processes for the indication and reduction in the incidence of vision-threatening injuries.

Neuronal Dysexcitability May Be a Biomarker of Migraine: A Visual Evoked Potential Study.

We report neuronal sensitization and impaired habituation in migraine using pattern reversal visual evoked potential (PRVEP) and correlate these with clinical characteristics of migraine. Sixty-five migraineurs and 30 healthy controls were included. A detailed clinical examination was done and migraine characteristics, including migraine trigger, photophobia, phonophobia, and allodynia were noted. Consecutive 5 blocks of PRVEP were recorded averaging 100 epochs at 3 Hz stimuli. The amplitude of N75 and P100 were measured. Amplitude of first block was considered for sensitization, and impaired habituation was considered if any subsequent block was not suppressed. Migraineurs had sensitization of P100 (14.01 ± 6.02 vs 11.60 ± 5.17 µV; P = .049), but not of N75 (42.22 ± 4.79 vs 11.08 ± 4.56 µV; P = .27) compared with the controls. Impaired habituation of N75 was more marked and persisted up to fourth block of VEP recoding. Impaired habituation of P100 was significant only in the third block. Baseline N75 and P100 amplitudes were higher in females, and N75 was also higher in those with longer duration of illness. These phenomena did not correlate with visual triggers. Sensitization and impaired habituation were marked during headache. Based on the PRVEP findings, it may be concluded that migraineurs have sensitization of P100 and impaired habituation of N75 especially during headache. These phenomena may be useful for therapeutic monitoring.

Relationship of high blood lactate levels with latency of visual-evoked potentials.

We studied, in healthy adult subjects, the association of high blood lactate levels, induced with an exhaustive exercise (12 subjects) or an intravenous infusion (four subjects) of a lactate solution (3 mg/kg in 1 min), with amplitude and latency of visual-evoked potentials. Amplitude of N75, P100, and N145 components did not show significant changes, whereas latency of P100 was reduced at exercise's end and that of N145 increased 10 min after the conclusion. Therefore, an increase of blood lactate induced by an exhaustive exercise or an intravenous infusion appears to induce an improvement in the conduction time between eye and striate cortex, while it seems to evoke a worsening of intracortical communication between striate and extrastriate areas.

P3-5: Temporal Interactions between Binocular Inputs in Visual Evoked-Potentials

The interaction between neural activity driven by inputs through the two eyes were examined using visual evoked-potentials (VEP) in normal human subjects. VEP recordings were obtained at the occipital electrodes using binocularly asynchronous pattern-reversal checkerboard stimuli: The patter-reversal times for the two eyes differed by 0, ±50, ±150, or ±350 ms, with the positive stimulus-onset asynchrony (SOA) meaning that the right-eye reversal occurred first. For comparison, monocular VEPs were also obtained using trial conditions where the checkerboard pattern-reversals were shown to only one eye, while a blank field to the other. The VEPs of the various trial conditions were analyzed using both temporal and frequency analysis methods. Three observations were made: First, the N75 amplitude was significantly reduced in the ±50 ms SOA conditions. Second, on ±150 ms and ± ms SOA conditions, a negative potential was observed over the period when the stimuli were binocularly incongruent. Third, the alpha-ban...

Repeatability of short-duration transient visual evoked potentials in normal subjects

To evaluate the within-session and inter-session repeatability of a new, short-duration transient visual evoked potential (SD-tVEP) device on normal individuals, we tested 30 normal subjects (20/20 visual acuity, normal 24-2 SITA Standard VF) with SD-tVEP. Ten of these subjects had their tests repeated within 1–2 months from the initial visit. Synchronized single-channel EEG was recorded using a modified Diopsys Enfant™ System (Diopsys, Inc., Pine Brook, New Jersey, USA). A checkerboard stimulus was modulated at two reversals per second. Two different contrasts of checkerboard reversal patterns were used: 85% Michelson contrast with a mean luminance of 66.25 cd/m2 and 10% Michelson contrast with a mean luminance of 112 cd/m2. Each test lasted 20 s. Both eyes, independently and together, were tested 10 times (5 times at each contrast level). The following information was identified from the filtered N75-P100-N135 complex: N75 amplitude, N75 latency, P100 amplitude, P100 latency, and Delta Amplitude (N75-P100). The median values for each eye’s five SD-tVEP parameters were calculated and grouped into two data sets based on contrast level. Mean age was 27.3 ± 5.2 years. For OD only, the median (95% confidence intervals) of Delta Amplitude (N75-P100) amplitudes at 10% and 85% contrast were 4.6 uV (4.1–5.9) and 7.1 uV (5.15–9.31). The median P100 latencies were 115.2 ms (112.0–117.7) and 104.0 ms (99.9–106.0). There was little within-session variability for any of these parameters. Intraclass correlation coefficients ranged between 0.64 and 0.98, and within subject coefficients of variation were 3–5% (P100 latency) and 15–30% (Delta Amplitude (N75-P100) amplitude). Bland–Altman plots showed good agreement between the first and fifth test sessions (85% contrast Delta Amplitude (N75-P100) delta amplitude, mean difference, 0.48 mV, 95% CI, −0.18–1.12; 85% contrast P100 latency delay, −0.82 ms, 95% CI, −3.12–1.46; 10% contrast Delta Amplitude (N75-P100) amplitude, 0.58 mV, 95% CI, −0.27–1.45; 10% contrast P100 latency delay, −2.05 mV, 95% CI, −5.12–1.01). The inter-eye correlation and agreement were significant for both SD-tVEP amplitude and P100 latency measurements. For the subset of eyes in which the inter-session repeatability was tested, the intraclass correlation coefficients ranged between 0.71 and 0.86 with good agreement shown on Bland–Altman plots. Short-duration transient VEP technology showed good within-session, inter-session repeatability, and good inter-eye correlation and agreement.

High test–retest reliability of checkerboard reversal visual evoked potentials (VEP) over 8 months

The inter-individual variation in the shape of a visual evoked potential (VEP) is large even for simple stimuli. We compared the inter-individual variation in VEP waveform to the intra-individual stability. We recorded VEP with checkerboard stimulation in 10 women aged 19-29years in two sessions. We determined the latencies and the peak-to-peak amplitude of N75 and P100. As a new approach in VEP research, we regressed VEP waveforms pairwise onto each other and calculated a t-value between all sessions. The maximal t-value was taken to indicate recognition for all 19 comparisons performed with one session. The recognition rate was cross-validated in a generalized linear regression model (GLM). The number of sessions correctly matched to the correct subject was 19 of 20 (true positives) leading to a sensitivity of 95.0% with confidence interval [75.1% 99.9%] for the method. The number of true negatives was 359 of 360 leading to a specificity of 99.7% [98.5% 100.0%]. The VEP waveform shows high intra-individual stability compared to the inter-individual variation in healthy women. With a new statistical approach the effect of external factors on the VEP waveform can now be contrasted against the normal variability over time in longitudinal studies.

Dependence of the Parameters of Visual Evoked Potentials on the Parameters of a Complex Visual Stimulus (Tests on Humans)

We recorded visual evoked potentials, VEP, elicited by presentation of a reversal chess pattern; 35 healthy persons were examined. A recording electrode was in point Oz, according to the 10-20 system; dimensions of the chess pattern square fields and their contrast varied from 1.8 to 120′ and from 2 to 100%, respectively. Peak latencies, PL, of the N75 component depended on the contrast of stimulus elements in a U-like manner with the minimum within a 20-25% range. The PL of the P100 component monotonically increased with a decrease in the contrast, while the dependence of the PL of N145 was complex: a trend toward a decrease with a decrease in contrast to 30%, a local maximum in about 25%, a decrease and stabilization within a 15-4% range, and a sharp increase at the minimum contrast. The amplitude of N75 decreased with decrease in contrast down to 20-25% and then stabilized; the amplitude of P100 decreased in an S-like mode, with a plateau within 25-4%. The dependence of the N145 amplitude was complex, with a plateau-like maximum at 30-15% contrast. The amplitudes of the negative VEP components, N75 and N145, increased with an increase in the square dimensions to 7.5′ and then decreased. Changes in the P100 amplitude included two phases, with a local minimum within an angular dimension range of 30-15O. The PL of all analyzed components in general increased with a decrease in the angular dimension of the pattern components. The above data are discussed considering concepts on the genesis of different VEP components and on the existence of specialized channels in the visual system, which are responsible for detection of different parameters of a visual object. The complex dynamics of the PL of the analyzed VEP components and of the P100 amplitude related to variation of the contrast and angular dimensions of the elements of a complex stimulus are considered to be determined by a module principle of the organization of the elements constituting different levels of the visual system and by transformations of the receptive fields of these elements on the level of cortical modules, which are related to changes in the stimulus parameters.