Visual evoked Potential (VEP):
Physiological variation in normal children and adolescent up to 20
years of age
Wadhera J1, Dudhmal V2
1Dr Jyoti Wadhera, Assistant Professor, Department of Physiology, 2Dr
Vandana Dudhmal, Associate Professor, Department of Physiology. Both
are affiliated with KD Medical College Hospital and Research Center,
Mathura, UP, India
Address for correspondence:
Dr Jyoti Wadhera, Email: jyotiwadhera@gmail.com
Abstract
Manuscript received:
1st Jan2015, Reviewed:
6th Jan 2015
Author Corrected:
15th Jan 2015, Accepted
for Publication: 3rd Feb 2015
Introduction
Visual evoked Potential is the electrical potential difference recorded
from the surface of scalp in response to Visual stimuli. It represents
a resultant response of cortical as well as subcortical areas to
photostimulation. Although various studies have been done on visual
evoked potential but there are few studies from India only. Therefore
this study was planned to study visual evoked potentials by recording
battery of N70, P100 & N155 waveform in different age groups of
normal healthy children. Methods: Present study was conducted in
department of Physiology of Tertiary care teaching hospital. 50 healthy
patients were included in two groups, below 5 years and 6- 20 years.
Visual evoked Potential has been recorded and their physiological
Variation has been observed. Results: It was seen that mean value and
standard deviation of amplitude of N70 wave in left eye showed
significant decrease in age group of 4 to 5 years. Mean value and
standard deviation of amplitude of P 100 wave in right eye showed
significant decrease in age group of 4 to 5 years. Other values were
not significant. Conclusion: Age and sex have little impact on Visual
evoked Potential in children. Eye dominance has been observed more
commonly.
Key words:
Visual evoked Potential, N70 latency in children, P100 amplitude in
children
Introduction
The record of electrical events that occurs in cerebral cortex after
stimulation of a sense organ is called evoked potentials (EPs) [1].
Evoked Potential test help to diagnose nervous system abnormalities,
hearing loss & assess neurological functions [2]. These are
useful as an index of cognitive functions in both health &
disease [3]. Major type of evoked potential tests are 1. Visual evoked
potential (VEP), 2. Brainstem auditory evoked Potential (BAEP), 3.
Somatosensory evoked Potential (SSEP).
Visual evoked Potential is the electrical potential difference recorded
from the surface of scalp in response to Visual stimuli. It represents
a resultant response of cortical as well as subcortical areas to
photostimulation [4]. It was first observed by Adrian and Mathews that
fleshing light can induce a stimulus dependent change of brain activity
[5]. VEP is primarily a reflection of activity originating in the
central 3° to 6 ° of visual field, which is relayed to
the surface of occipital lobe. The transient VEPs consist of series of
waveforms of opposite polarity, the negative waveform is denoted as N
and positive waveform is denoted as P, which is followed by the
approximate latency in millisec [6]. The commonly use waveform are N70,
P100 and N155. The P100 waveform of VEP is generated in occipital
cortex due to activation of primary visual cortex and also due to
thalamocortical fibers. N70 refelects the activity of fovea and primary
visual cortex while N155 reflects the activity of visual association
areas 18 & 19 [4].
VEP has been influenced by various factors. Age has been reported to
influence latency of P100 at a rate of 2.5 ms/decade after 5th decade
[7]. Iinfant and young children latency is longer and reaches adult
value by 5-6 years. In infants amplitude is almost double of adult
value [4]. Various studies on VEP have shown variation in VEP with age
and sex in pediatric population. N1 amplitude increases significantly
with age, whereas N1 latency showed a small age related decrease [8].
Some studies reported no gender and eye differences in VEP latency and
amplitude [9]. Although various studies have been done on visual evoked
potential but there are few studies from India only. Therefore this
study was planned to study visual evoked potentials by recording
battery of N70, N100 & N155 waveform in different age groups of
normal healthy children. Study also comprises the differences in visual
evoked potentials in relation to gender and eye dominance.
Material
& Methods
Present study was conducted in department of Physiology of Tertiary
care teaching hospital. 50 healthy patients were included in two groups
Group 1: 4 to 5 years of age
Group 2: 6 to 20 years
Children below 4 years were excluded from study because they could not
cooperate in maintaining fixation of eye at central point of checker
board screen. This is an important pre requisite for recording pattern
visual evoked potential [9]. Procedure of VEP recording: VEP were
recorded in all subjects on a particular machine under similar
laboratory conditions after they were acclimatize to the experimental
conditions. The nature of the test was explained to them to allay fear
and apprehension. The subject were informed about study and written and
Verbal consent was taken.
Visual evoked Potential recordings were performed in a dark and sound
attenuated room in a laboratory. The subject was asked to sit
comfortably in front of the checkerboard pattern at an eye- screen
distance of 100 cm. The stimulus pattern was a black and white
checkerboard displayed on a computer screen. The checks alternate from
black/white at the rate of approximately twice per second. The subject
was instructed to gaze at red color dot on the centre of checkerboard
pattern. Each eye was tested separately. Every time when there was
alteration in the pattern, the subject visual system generated an
electrical response which was recorded using electrode [10].
For performing VEP test standard disc EEG electrode were used. These
electrode were made of standard silver surface connected to a
wire which was plugged into the machine [6].
The skin was prepared by degreasing. The recording electrode was place
at highest point on the occiput using the conduction jelly or electrode
paste. [OZ electrode was located in the middle of the variation zone of
calcarine fissure i.e. at the highest point on the occiput].
Results
TABLE 1: Showing Mean
Value, Standard Deviation and Statistical Significance of Amplitude
(v) and Latency(ms) of N70 Waveform Between Group I and
Group II
|
|
Group
I
|
Group
II
|
P-value
|
|
Left
|
Right
|
Left
|
Right
|
Left
|
Right
|
|
N70
Amplitude(mv)
|
|
Mean
|
11.5
|
11.8
|
13.6
|
12.25
|
0.049*
|
>0.05NS
|
|
±
SD
|
2.97
|
2.75
|
4.27
|
3.91
|
|
|
|
N70
Latency(ms)
|
|
Mean
|
63.74
|
66.28
|
63.84
|
64.64
|
>0.05NS
|
>0.05NS
|
|
±
SD
|
4.29
|
4.97
|
3.5
|
4.85
|
|
|
*statistically significant; NS-not significant
Table depicts that mean value for amplitude of N70 wave between group 1
and 2 is statistically significant in left eye.
TABLE 2: Showing Mean
Value, Standard Deviation and Statistical Significance of Amplitude
(v) and
|
|
Group
I
|
Group
II
|
P-value
|
|
Left
|
Right
|
Left
|
Right
|
Left
|
Right
|
|
P100
Amplitude(mv)
|
|
Mean
|
13.1
|
41.2
|
14.4
|
16.9
|
>0.05NS
|
0.027
|
|
±
SD
|
3.32
|
4.19
|
2.42
|
4.16
|
|
|
|
P100
Latency(ms)
|
|
Mean
|
94.66
|
93.44
|
96.7
|
96.52
|
>0.05NS
|
>0.05NS
|
|
±
SD
|
7.52
|
7.27
|
7.31
|
9.68
|
|
|
|
P100
duration (ms)
|
|
Mean
|
76.2
|
81.0
|
81.0
|
80.4
|
>0.05NS
|
>0.05NS
|
|
±
SD
|
11.39
|
9.68
|
9.68
|
8.52
|
|
|
*statistically significant; NS-not significant
Table depicts that mean value for amplitude of P100 wave between group
1 and 2 is statistically significant in right eye. All other parameters
are statistically insignificant.
TABLE 3: Showing Mean
Value, Standard Deviation and Statistical Significance of Amplitude
(v) and
|
|
Group
I
|
Group
II
|
P-value
|
|
Left
|
Right
|
Left
|
Right
|
Left
|
Right
|
|
P155
Amplitude(mv)
|
|
Mean
|
12.4
|
13.2
|
11.7
|
14.75
|
>0.05NS
|
>0.05NS
|
|
±
SD
|
3.85
|
4.24
|
3.44
|
4.85
|
|
|
|
N155
Latency(ms)
|
|
Mean
|
154.48
|
157.5
|
154.15
|
152.76
|
>0.05NS
|
0.01*
|
|
±
SD
|
8.62
|
7.12
|
5.13
|
5.13
|
|
|
*statistically significant; NS-not significant
Table depicts that mean value for latency of N155 wave between group 1
and 2 is statistically significant in right eye. All other parameters
are statistically insignificant.
TABLE 4: Showing Mean
Value, Standard Deviation and Statistical Significance of Amplitude
(v) and
|
|
Male
|
Female
|
P-value
|
|
Left
|
Right
|
Left
|
Right
|
Left
|
Right
|
|
N70
Amplitude
|
|
Mean
|
10.38
|
10.76
|
12.7
|
12.91
|
0.049*
|
0.049*
|
|
±
SD
|
2.46
|
2.57
|
3.1
|
2.57
|
|
|
|
N70
Latency
|
|
Mean
|
61.79
|
66.83
|
65.85
|
65.68
|
0.014*
|
>0.05NS
|
|
±
SD
|
3.97
|
5.2
|
3.68
|
4.85
|
|
|
*statistically significant; NS-not significant
The data depicts that mean value for amplitude of N70 wave between male
and female children in group 1 is statistically significant in both
eyes. Latency is significantly different in left eye only..
TABLE 5: Showing Mean
Value, Standard Deviation and Statistical Significance of
Amplitude (v), Latency(ms) and Duration (ms) of P100 Waveform Between
Males and
|
|
Male
|
Female
|
P-value
|
|
Left
|
Right
|
Left
|
Right
|
Left
|
Right
|
|
P100
Amplitude
|
|
Mean
|
11.34
|
11.53
|
15.0
|
17.08
|
0.004**
|
0.000***
|
|
±
SD
|
1.94
|
2.4
|
3.53
|
3.81
|
|
|
|
P100
Latency
|
|
Mean
|
93.43
|
92.16
|
95.98
|
94.82
|
>0.05NS
|
>0.05NS
|
|
±
SD
|
5.75
|
5.51
|
9.14
|
9.79
|
|
|
|
P100
Duration
|
|
Mean
|
75.0
|
79.61
|
77.5
|
82.5
|
>0.05NS
|
>0.05NS
|
|
±
SD
|
12.24
|
11.2
|
10.76
|
7.83
|
|
|
*statistically significant; NS-not significant; **/***-highly
significant
The data depicts that mean value for amplitude of P100 wave between
male and female children in group 1 is statistically significant in
both eyes.
TABLE 6: Showing Mean
Value, Standard Deviation and Statistical Significance of Amplitude
(v) and Latency(ms) of N155 Waveform between Males and Females of
Group I
|
|
Male
|
Female
|
P-value
|
|
Left
|
Right
|
Left
|
Right
|
Left
|
Right
|
|
N155
Amplitude
|
|
Mean
|
11.53
|
12.88
|
13.33
|
13.54
|
>0.05NS
|
>0.05NS
|
|
±
SD
|
4.15
|
5.18
|
3.42
|
3.10
|
|
|
|
N155
Latency
|
|
Mean
|
152.03
|
156.24
|
157.15
|
158.87
|
>0.05NS
|
>0.05NS
|
|
±
SD
|
5.49
|
7.70
|
10.69
|
6.49
|
|
|
The data depicts that mean value for amplitude and latency
of N155 wave between male and female children in group 1 is
statistically non-significant in both eyes.
TABLE 7: showing Mean
Value, Standard Deviation and Statistical Significance of Amplitude
(v) and
|
|
Male
|
Female
|
P-value
|
|
Left
|
Right
|
Left
|
Right
|
Left
|
Right
|
|
N70
Amplitude
|
|
Mean
|
13.54
|
12.39
|
13.65
|
12.11
|
>0.05NS
|
>0.05NS
|
|
±
SD
|
3.91
|
4.72
|
7.74
|
3.20
|
|
|
|
N70
Latency
|
|
Mean
|
64.81
|
66.12
|
62.95
|
6.27
|
>0.05NS
|
>0.09**
|
|
±
SD
|
3.27
|
3.27
|
3.59
|
1.50
|
|
|
*statistically significant; NS-not significant
The data depicts that mean value for latency of N70 wave between male
and female children in group 2 is statistically significant in right
eyes only.
TABLE 8: Showing Mean
Value, Standard Deviation and Statistical Significance of Amplitude
(v) and Latency(ms) and Duration (ms) of P100Waveform between Males
and
|
|
Male
|
Female
|
P-value
|
|
Left
|
Right
|
Left
|
Right
|
Left
|
Right
|
|
P100
Amplitude
|
|
Mean
|
14.37
|
18.12
|
14.42
|
15.76
|
>0.05NS
|
>0.05NS
|
|
±
SD
|
3.39
|
4.66
|
1.09
|
3.44
|
|
|
|
P100 latency
|
|
Mean
|
101.10
|
99.8
|
92.73
|
93.5
|
0.002**
|
0.27*
|
|
±
SD
|
4.48
|
5.68
|
7.21
|
7.45
|
|
|
*statistically significant; NS-not significant; **-highly significant
The data depicts that mean value for latency of P100 wave between male
and female children in group 2 is statistically significant in both
eyes.
TABLE 9: Showing Mean
Value, Standard Deviation and Statistical Significance of Amplitude
(v) and
|
|
Male
|
Female
|
P-value
|
|
Left
|
Right
|
Left
|
Right
|
Left
|
Right
|
|
N155
Amplitude
|
|
Mean
|
11.45
|
16.35
|
11.92
|
13.26
|
>0.05NS
|
>0.05NS
|
|
±
SD
|
3.44
|
4.37
|
3.55
|
4.93
|
|
|
|
N155
Latency
|
|
Mean
|
156.43
|
154.98
|
152.06
|
150.72
|
>0.05NS
|
>0.35*
|
|
±
SD
|
5.88
|
5.21
|
4.79
|
4.28
|
|
|
*statistically significant; NS-not significant
The data depicts that mean value for latency of N155 wave between male
and female children in group 2 is statistically significant in right
eye.
Discussion
The VEP should be regarded as complementary to clinical examination and
neuro- ophthalmological investigations [6]. It is an important tool for
diagnosis of neurological and ophthalmological disorders [11]. VEP are
helpful in detecting blindness in patients who can not communicate like
young infants and children. If repeated stimulation of visual field
causes no change in potentials, then subjects brain is not receiving
any signals from his or her eyes. In optic neuritis signals are
delayed. VEP are also used in investigating basic function of visual
perceptions.
VEP are computer generated average brainwave responses to visual
stimuli which may be performed in various clinical scenario.
Furthermore infants and children with retinal disorder, eye movement
disorder, optic nerve dysfunction, delayed visual development, cortical
blindness and neurological disorder with ophthalmological manifestation
can be assessed [11]. VEP can also measure optic nerve
function pre and post craniofacial surgery, which involve manipulation
of facial bones. Tondon et al in his study in school going children
between 4 to 15 years used two sets of 256 stimuli with check size 32
alteration rate 1 HZ to each eye and VEP were analyzed. The latency of
various components of VEP along with P amplitudes were recorded for
right and left eye separately in boys and girls. The normative data was
reported and does not show eye and gender differences in children [9].
Fenwick et studied visual evoked response to pattern reversal stimulus
latency in 73 children aged between 6 to 11 years. Analysis of data
showed that there is no clear relationship between the mean amplitude
or latency of evoked response and age. However significant changes were
found between linear displacement and linear age for the N65-P95 wave
and there was a complex interaction for the same wave between age, sex
and eye. There were significant differences in latencies between right
and left eye between boys and girls, with boys having longer latency.
There were thus both age and sex related differences in the amplitude
and N65-P95 wave in 6-11 year old children were observed [12]. In
another study conducted on 85 children between 8-15 years to explore
the effect of flash intensity and age on evoked potentials revealed N1
amplitude increased significantly with age, whereas N1 latency showed a
small age related decrease [8].
Visual process continue to mature well into childhood due to the
development of the retina, optic nerve, visual pathway and visual
cortex. A study conducted on 41 children from 1.5 months to
7.5 years for visual evoked potential latencies and amplitudes were
evaluated to flash, reversal and onset stimulation. Age dependent
exponential decrease in latencies to flash, reversal and onset
stimulation were seen. For amplitude there was only age dependent
increase to onset stimulation. There was a significant correlation
between visual evoked potentials and visual aquity for latencies to
flash, reversal and onset stimulation [13].
In our study on comparison of group A and B, It was seen that
mean value and standard deviation of amplitude of N70 wave in left eye
showed significant decrease in age group of 4 to 5 years. No
statistically significant difference was seen in value of latencies of
N70 wave in both the eyes in groups. It was observed that
mean value and standard deviation of amplitude of P 100 wave in right
eye showed significant decrease in age group of 4 to 5 years. No
statistically significant difference was seen in value of latencies and
duration of N100 wave has been observed. No statistically significant
difference was seen in value of amplitude of N155 wave between both
groups. It was observed that mean value and standard deviation of
latency of N155 wave in right eye in age group of 4 to 5 years was
statistically significant.
Conclusion
Age has significantly variable effects on visual evoked potentials
beyond the age of 20 years. In children effect is less prominent.
Gender has some effect in adolescent only not in young children below 5
years of age. Significantly longer latencies and lower amplitude has
been observed in male.
Funding:
Nil, Conflict of
interest: None initiated.
Permission from IRB:
Yes
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How
to cite this article?
Wadhera J , Dudhmal V. Visual evoked Potential (VEP): Physiological
variation in normal children and adolescent up to 20 years of age. Int
J Med Res Rev 2015;3(3):335-340. doi: 10.17511/ijmrr.2015.i3.067.