Influence of visual angle on pattern reversal visual evoked potentials

Abstract

Purpose:The aim of this study was to find whether the visual evoked potential (VEP) latencies and amplitude are altered with different visual angles in healthy adult volunteers or not and to determine the visual angle which is the optimum and most appropriate among a wide range of check sizes for the reliable interpretation of pattern reversal VEPs (PRVEPs).Materials and Methods:The present study was conducted on 40 healthy volunteers. The subjects were divided into two groups. One group consisted of 20 individuals (nine males and 11 females) in the age range of 25-57 years and they were exposed to checks subtending a visual angle of 90, 120, and 180 minutes of arc. Another group comprised of 20 individuals (10 males and 10 females) in the age range of 36-60 years and they were subjected to checks subtending a visual angle of 15, 30, and 120 minutes of arc. The stimulus configuration comprised of the transient pattern reversal method in which a black and white checker board is generated (full field) on a VEP Monitor by an Evoked Potential Recorder (RMS EMG. EPMARK II). The statistical analysis was done by One Way Analysis of Variance (ANOVA) using EPI INFO 6.Results:In Group I, the maximum (max.) P100 latency of 98.8 ± 4.7 and the max. P100 amplitude of 10.05 ± 3.1 μV was obtained with checks of 90 minutes. In Group II, the max. P100 latency of 105.19 ± 4.75 msec as well as the max. P100 amplitude of 8.23 ± 3.30 μV was obtained with 15 minutes. The min. P100 latency in both the groups was obtained with checks of 120 minutes while the min. P100 amplitude was obtained with 180 minutes. A statistically significant difference was derived between means of P100 latency for 15 and 30 minutes with reference to its value for 120 minutes and between the mean value of P100 amplitude for 120 minutes and that of 90 and 180 minutes.Conclusion:Altering the size of stimulus (visual angle) has an effect on the PRVEP parameters. Our study found that the 120 is the appropriate (and optimal) check size that can be used for accurate interpretation of PRVEPs. This will help in better assessment of the optic nerve function and integrity of anterior visual pathways.

Visual Evoked potential signal processing and analysis for normal and galucomic eyes

“…In contrast, Kathari et al, (15) found statistically significant difference of amplitude of N135 for the checks (15', 30' and 120'),and observed that high value of mean P100 amplitude for usual angle 15' and when the angle increased to 30' a drop of P100 amplitude was obtained with increasing check size.…”

“…On comparison between blue and white FVEP in latencies and amplitudes (COVinter) and (COVintra ) were less for blue FVEP than for white FVEP, this means that blue light has less variability. Concerning PRVEP, the mean latencies of (N75, P100, N135) and amplitudes of (N75-P100) and (P100-N135) using four different check sizes (15,30, 60 and 120) minutes of arc and the obtained results are tabulated in table (5,6) and summarized by histograms in figure (7,8) respectively .The mean of all latencies were decreased with increase of check size and the amplitudes were increased when the check size increase. It is to be noted that the most suitable visual angle was 120'.…”

“…In glaucoma group, there were latencies rising and amplitudes reduction in both flash VEP (white and blue) and PRVEP (in different 4 check sizes) when compared with healthy group. The results for two groups are summarized by histograms in Figures (13,14,15,16) respectively.…”

Different check sizes pattern-reversal visual evoked potentials study in patients with compensated hepatic cirrhosis

“…In our study, the 15 min check size had revealed additional information than the 1 degree check size and that could delineate the different area of perception of both check sizes. The Large check sizes 1 degree (60 min) mainly perceive signals from the peripheral field outside the central 3º but not beyond 10º of the visual field Phurailatpam, 2014, while smaller check sizes mainly perceive signal from the foveal area (central visual field) Kothari et al, 2014. Jancic et al, 2016 demonstrated that the responses to smaller checks are more sensitive to disorders of the visual pathway.…”

“…Magnocellular (M pathway), which is sensitive to low spatial frequency (large checks) and parvocellular ( P pathway), which is more sensitive to high spatial frequency (small checks). Kothari et al, 2014 ;Abdelkader, 2016. VEPs are influenced by optic nerve diseases, demyelinating processes, disorders of either subcortical or cortical neurons of brain hemispheres, metabolic abnormalities, traumatic brain injury and the use of psychoactive medications. Amodio & Montagnese,2015, the magnitude of the PVEP abnormality is correlated with other measures of injury severity such as the extent of cognitive impairment.…”