|Year : 2016 | Volume
| Issue : 1 | Page : 37-40
Multifocal visual evoked potential normative scaling in Egyptian adolescents
Elham N Fayed1, Neveen M El-Fayoumy1, Mohamed M Al-Kanishy2, Hossam Mohammed3, Mona M Nada1, Amira M El Gohary1, Zeinab S El-Sanabary3, Saly H Elkholy1
1 Department of Clinical Neurophysiology, Cairo University, Cairo, Egypt
2 Department of Ophthalmology, Cairo University, Cairo, Egypt
3 Paediatric Diabetic Unit, Cairo University, Cairo, Egypt
|Date of Submission||23-Apr-2015|
|Date of Acceptance||28-Aug-2015|
|Date of Web Publication||15-Feb-2016|
Elham N Fayed
Department of Clinical Neurophysiology, Cairo University, 11571 Cairo
Source of Support: None, Conflict of Interest: None
The multifocal visual evoked potential (mfVEP) is a useful tool for evaluating optic nerve disease and visual defects secondary to optic nerve or retinal ganglion cell damage.
The aim of this study was to establish technical guidelines and normative values of the peak time and amplitude of the mfVEP in adolescents.
Participants and methods
This is a prospective study conducted on 20 healthy adolescents (40 eyes) 10 girls and 10 boys. Their age ranged between 10 and 15 years with a mean of 12.50 1.48. Monocular mfVEP was obtained from each eye separately. The peak time and amplitude of the P1 wave of each individual response were measured and then expressed in the form of four quadrants.
The peak time and amplitude of the P1 wave showed no statistical differences between the four quadrants and no correlation to the age. There were no statistically significant differences between girls and boys or between left and right eyes regarding the peak time and the amplitude of the P1 wave.
We obtained normative data of mfVEP of the adolescents in our lab as a preliminary work for further application in different neuro-ophthalmological disorders.
Keywords: Adolescents, amplitude, multifocal visual evoked potential, normal range, peak time
|How to cite this article:|
Fayed EN, El-Fayoumy NM, Al-Kanishy MM, Mohammed H, Nada MM, El Gohary AM, El-Sanabary ZS, Elkholy SH. Multifocal visual evoked potential normative scaling in Egyptian adolescents. Egypt J Neurol Psychiatry Neurosurg 2016;53:37-40
|How to cite this URL:|
Fayed EN, El-Fayoumy NM, Al-Kanishy MM, Mohammed H, Nada MM, El Gohary AM, El-Sanabary ZS, Elkholy SH. Multifocal visual evoked potential normative scaling in Egyptian adolescents. Egypt J Neurol Psychiatry Neurosurg [serial online] 2016 [cited 2021 Apr 20];53:37-40. Available from: http://www.ejnpn.eg.net/text.asp?2016/53/1/37/176369
| Introduction|| |
The development of the multifocal visual evoked potential (mfVEP) has lagged behind the multifocal electroretinogram (mfERG). The large intersubject variability in mfVEP responses has discouraged its use for a period of time . Its usefulness has been extended with the development of an automated, computerized method of measuring the latency of the local mfVEP responses ,. ISCEV (2011) provides guidelines for recording mfERG and recommended each lab to develop its own normative values for clinical use . However till now, there is no international guideline to standardize the use of mfVEP in clinical practice. Balachandran et al. (2004)  were concerned with the maturation of the mfVEP in children. They observed maturation of latency and amplitude until the age of 13 years, which may be a reflection of greater recruitment of neurons in the striate cortex.
The diagnostic utility in evaluating optic diseases and visual defects secondary to optic nerve or retinal ganglion cell damage can be enhanced by combining the use of mfVEP with mfERG . The use of multifocal modalities in pediatric age groups has been limited by the intolerance of the children to the techniques and the effect of eccentric fixation . Use of mfVEP in adolescents is another challenging point. Developing lab normative data will help in extending our work to include different diseases affecting the visual system as diabetes mellitus and retinal diseases in such particular age group.
| Aim of work|| |
The aim of this study was to establish technical guidelines and normative values of the peak time and amplitude of the mfVEP in normal adolescents.
| Participants and methods|| |
This is a prospective study conducted on 20 healthy adolescents (40 eyes) 10 girls and 10 boys. Their age ranged between 10 and 15 years with a mean of 12.50 ± 1.48 years. Approval of the research ethics committee of the Faculty of Medicine, Cairo University was taken in November 2013. Informed written consent was taken from each parent or guardian after full explanation of the aim of the study and the methodology which will be used.
Slit-lamp biomicroscopy (slit-lamp Haag-Streit machine, Koeniz, Switzerland) was performed for all participants to exclude anterior segment diseases. Fundus examination was done under full pupillary dilatation to exclude posterior segment pathology (retinal or optic nerve diseases). The best distance vision (with eyeglasses if used) for all participants was not less than 6/9 using Snellen chart. mfVEP was done using the Reti-Scan 21 (Roland Consult, Brandenburg a.d. Havel, Germany). mfVEP technique: the recording electrodes used were VEP cross-connection [Figure 1] with a bridge electrode connection; electrode A was 2 cm above the inion and electrode C was 1 cm below the inion. Electrodes B and D were 1 cm above and 4 cm lateral to inion respectively. The ground electrode was placed over the forehead by using a rubber band. All electrodes were soaked in water and soap before starting application. In addition, forehead and scalp were cleaned by cleaning gel (Nuprep) and then by soap and water to get the best conductivity. The impedance was kept below 10 kW. The pupil of the examined eye should not be dilated with average size of 4 mm. The fellow eye was occluded with light pressure to prevent blinking artifacts. The adolescent was instructed to fixate his/her eye to a small black cross in the center of the stimulating screen. The stimulus consisted of 61 segments, each with 16 checks (eight white and eight black). The luminance values for the black and white checks were 2 and 200 cd/m 2 respectively, while the background was set to 100 cd/m 2 . The viewing angle was 30° and presented on a 20 inch LCD monitor at a viewing distance of 33 cm. Low and high amplifier cutoffs were set to 3 and 100 Hz respectively. Each eye session lasted for about 8 min with a video monitoring fixation check. To improve fixation, each session was broken into four cycles. An artifact level of 10% was accepted for a reliable examination. Raw trace data were analyzed with peak-to-trough amplitude and peak time of P1 wave. The amplitude and peak time of average P1 wave for the four quadrants were calculated.
|Figure 1: Stimulating screens of the multifocal visual evoked potential (VEP) with the cross-connection recording electrodes applied to a 12-yearold boy.|
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Abbreviation of quadrants
Q1: lower nasal, Q2: upper nasal, Q3: upper temporal, Q4: lower temporal [Figure 2].
|Figure 2: Quadrants, divisions of the multifocal visual evoked potential (VEP) from the left eye.Q1: lower nasal (red), Q2: upper nasal (green), Q3: upper temporal (orange), Q4: lower temporal (olive).|
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The data were coded and entered using the statistical package SPSS version 15. The data were summarized using descriptive statistics: mean, SD, minimal and maximal values for quantitative variables and numbers. Statistical differences between groups were tested using independent sample t-test for quantitative normally distributed variables while nonparametric Mann-Whitney test was used for quantitative variables which are not normally distributed. Correlations were done to test for linear relations between variables. P-values less than 0.05 were considered statistically significant.
| Results|| |
Data were tabulated for minimum, maximum, mean and SD for the peak time (ms) and amplitude (nV/deg) - of P1 wave - for each quadrant in mfVEP [Table 1]. There were no statistically significant differences between left and right eyes regarding the peak time and the amplitude of the P1 wave mfVEP tests.
mfVEP-P1-wave-peak time, comparative studies between the four quadrants were statistically insignificant (P > 0.05, [Table 1]). So we considered the normal accepted peak latency of the P1 wave for all quadrants to be ranged between 90 and 115 ms (mean ± 1 SD = 102.65 ± 12.39).
mfVEP-P1-wave-amplitude, comparative studies between the four quadrants were also statistically insignificant (P > 0.05, [Table 1]). So, the normal accepted amplitude of the P1 wave for all quadrants will be ranged between 2.5 and 5 nV/deg 2 (mean ± 1 SD = 3.5 ± 1.35).
No significant correlations could be found between either amplitude or peak time of P1 wave and the ages of the adolescents [Table 2].
|Table 2: Correlation between the average amplitude (nV/deg2), the peak time (ms) of P1 wave and the ages of the adolescents|
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| Discussion|| |
Enrollment of adolescents in this study was a challenge in itself. They must be convinced with the usefulness of the technique used and its validity. Most of them complained about the tightness of the rubber band used to fix the electrodes of the mfVEP taking a period to adapt to it. Fixation is not an issue in this age group. Interrupting the session can be minimized or increased according to the adolescent's cooperation.
There are two main sources of intersubject variability. First, the position of the calcarine fissure relative to the external landmarks varies among individuals . Second, individuals differ in the way the cortex is folded and how the primary visual area is positioned within these folds ,. If intersubject variability is due to cranio-occipital variations, the mfVEP responses from the two eyes should be identical. The reason for this is purely anatomical; any point in the visual field projects to the nasal retina of one eye and the temporal retina of the other, but both points project to essentially the same region of the striate cortex . In our work, mfVEP intersubject variability did not represent a great obstacle which may be due to the homogeneous group sample, the patience of the technician and the well experience of the examining doctor.
Raw trace data were analyzed for each wave within the interval of 60-220 ms determined and compared among channels for every stimulated segment of the visual field. Amplitude and latency for each field sector of the mfVEP is determined .
Peak latency between 90 and 115 ms is accepted as a normal range. The amplitude ranged from 2.5 to 5 nV/deg 2 . Less than 50% reduction of amplitude is the accepted limit of difference between quadrants.
There is no significant correlation between the age of the adolescents, sex, the eye laterality and the amplitude or the peak time of P1 wave in mfVEP test. The only available published work in the same age group to be compared with is that of Balachandran et al. (2004)  who tested 70 normal children between 5 and 16 years in whom the latency of the dominant peak showed a decrease with age reaching a plateau at 13 years of age which is almost the mean age of our adolescents. They had a large variation in full field amplitude between children, with no significant correlation with age. These findings suggest an increasing complexity of physiological response during maturation, extending at least into early adolescence. On the same hand, Wolff et al. (2010)  found minimal effect of age on mfVEP peak time and amplitude in their normal control between 25 and 45 years of age. Despite the large interindividual variation captured by Klistorner and Graham (2000) , the adult signal amplitude did not decline with age. They added that children under the age of 10 years had smaller signals than the adult ones. This point still needs further evaluation in a wider age range.
| Conclusion|| |
We obtained normative data of the mfVEP test of the adolescents in our lab as a preliminary step to apply multifocal tests as a diagnostic tool in different ophthalmologic, general and neurological diseases with ophthalmologic manifestation in such age group.
The authors are thankful to Mrs HalaEltoukhy, the nurse in the Ophthalmic Diagnostic and Laser Unit, Cairo University Hospitals, for her great effort.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2]
[Table 1], [Table 2]