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Effect of Ocular Dominance on the Latency and Amplitude of Visual Evoked Potentials

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Background: Ocular dominance is the tendency to prefer visual input from one eye to the other. VEPs are the electrical potentials recorded from the scalp in response to visual stimuli to assess conduction pathway from the retina to the occipital cortex. Objectives: 1. to determine ocular dominance. 2. To compare the latency and amplitude of Visual evoked potentials in dominant and non dominant eye. Materials & methods: Among 100 normal healthy subjects, Ocular dominance was determined by Miles & Porta test & then VEPs was recorded. Latency & amplitude of individual VEP wave parameters were measured. Results: Eye dominance by Porta & Miles test, showed Right eye dominant were 75% & left eye dominant 25%. Eye dominance on Amplitude is increased in dominant eye which is statistically significant compared to the non-dominant eye. Eye dominance on latency of N70 and P100 is decreased in dominant eye which is statistically significant compared to the non-dominant eye. Conclusion: The latency of N70 & P100 has been found to be lesser in the dominant eye and the amplitude is increased in the dominant eye as compared to non-dominant eye, which provides electrophysiological evidence of lateralization in the central nervous system.
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IOSR Journal of Dental and Medical Sciences (JDMS)
ISSN: 2279-0853, ISBN: 2279-0861. Volume 2, Issue 4 (Nov.- Dec. 2012), PP 19-24
www.iosrjournals.org
www.iosrjournals.org 19 | Page
Effect of Ocular Dominance on the Latency and Amplitude of
Visual Evoked Potentials
1Jagadamba .A, 2Karthiyanee kutty
1,2Department of Physiology,Sri Devaraj Urs Medical College, Tamaka, Kolar
Abstract: Background: Ocular dominance is the tendency to prefer visual input from one eye to the other.
VEPs are the electrical potentials recorded from the scalp in response to visual stimuli to assess conduction
pathway from the retina to the occipital cortex.
Objectives: 1. to determine ocular dominance.
2. To compare the latency and amplitude of Visual evoked potentials in dominant and non dominant eye.
Materials & methods: Among 100 normal healthy subjects, Ocular dominance was determined by Miles &
Porta test & then VEPs was recorded. Latency & amplitude of individual VEP wave parameters were measured.
Results: Eye dominance by Porta & Miles test, showed Right eye dominant were 75% & left eye dominant
25%. Eye dominance on Amplitude is increased in dominant eye which is statistically significant compared to
the non-dominant eye. Eye dominance on latency of N70 and P100 is decreased in dominant eye which is
statistically significant compared to the non-dominant eye.
Conclusion: The latency of N70 & P100 has been found to be lesser in the dominant eye and the amplitude is
increased in the dominant eye as compared to non-dominant eye, which provides electrophysiological evidence
of lateralization in the central nervous system.
Key words: Visual evoked potentials, ocular dominance
I. Introduction
Dominance of one member of a bilateral pair of bodily structures means a functional priority,
superiority, or preference of that member. Functional lateralization occurs in the paired organs of the body, such
as hands, legs, and cerebral hemispheres. Ocular dominance was first described in 1953 by Giovanni Battista
Porta. Ocular dominance, otherwise called eye dominance or eyedness was the tendency to prefer visual input
from one eye to the other [7, 13]. The eye is a sensory organ and has no conscious proprioception and vision in
each eye is represented bilaterally and equally in the occipital lobes. Individuals have no consciousness of using
right or left eye, as one is conscious of having left or right hand. An individual does not see the world from left
or right eye but from a single so called cyclopean eye, which combines information from both. Dominance wise
eyes work as ones hand. They grab the image with one eye and pass on to other and start to analyze the object
by refining like using their fingertips or balancing objects with two hands [1].
Around two-thirds of the population is right eye dominant, however neither eye is dominant in a small
portion of the population [2.3]. Dominance does appear to change depending upon direction of gaze due to
image size changes on the retinas [4]. Furthermore, the eye preferred for sighting does not indicate handedness.
This is not surprising since each eye projects to both cerebral hemispheres whereas each hand is represented
mainly in the opposite hemisphere.
In normal binocular vision there is an effect of parallax, and therefore the dominant eye is the one that
is primarily relied on for precise positional information. This may be particularly important in sports which
require aim, such as Archery, darts or shooting sports [5]. Ocular dominance is of great magnitude in predicting
patient satisfaction with mono vision correction in cataract surgery, refractive surgery and contact lens wear [6].
The dominant eye has higher degree of myopic refractive error and longer axial length than the non
dominant eye especially in patients with high amounts of anisometropia[14].
The repeated suppression of the non sighting eye to avoid physiologic diplopia and the weaker motoric
drive may predispose the non-dominant eye to amblyopia ex anopsia [8].
A directional dominance or sighting test can be done in various ways. For example, a patient will form
a hole with his hands and binocularly center an object in that hole. When he alternately occludes either eye, only
the dominant eye will still see the same object [10].
The VEP assess the functional integrity of the visual pathway from the receptors in the retina to the
occipital cortex. It measures the conduction of the visual pathways from the optic nerve, optic chiasm and optic
radiations to the occipital cortex. The most important fact to consider is that although the axons form the nasal
half of the retina decussate at the optic chiasm, the temporal axons do not. Therefore, retrochiasmatic lesions
Effect Of Ocular Dominance On The Latency And Amplitude Of Visual Evoked Potentials
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may not be detected by full-field checkerboard stimulation. VEPs are most useful in testing optic nerve function
and less useful in postchiasmatic disorders [9].
The VEPs has been used to study various physiological parameters,very few studies have been done to
compare the ocular dominance with visual evoked potentials.
So the aim of study is to determine ocular dominance and its effect on the latency and amplitude
components of Visual evoked potentials in dominant and non dominant eye in normal healthy subjects.
II. Materials And Methods
The Study group consisted of 100 normal healthy subjects aged 18-40 years with normal vision6/6 with
or without glasses who volunteered. Ethical clearance was obtained from Institutional Ethics Committee.
Informed consent was obtained. The exclusion criteria were subjects with visual impairment, history of use of
drug intake (mydriatics & myotics) & history of any chronic medical illness.
2.1. Methodology
During phase of the experiment, subjects were screened as per the criteria laid down under inclusion &
exclusion criteria. The informed consent was taken from selected subjects & they were given specific dates to
come to neurophysiology lab and hair washed without applying oil.
Data was collected after clinical examination visual acuity of 6/6 with normal visual fields was
ensured. On entering lab the subjects were explained about the procedure. Ocular dominance was determined by
Miles test and confirmed by Porta test and then the visual evoked potentials were recorded.
2.2. Miles Test
In this test the observer extends both arms, brings both hands together to create a small opening, then
with both eyes open views a distant object through the opening. The observer then alternates closing the eyes or
slowly draws opening back to the head to determine which eye is viewing the object, that is the dominant eye
[12].
2.3. Porta Test
The observer extends one arm, and then with both eyes open aligns the thumb or index finger with a
distant object. The observer than alternates closing the eyes or slowly draws the thumb/finger back to the head
to determine which eye is viewing the object ,that is the dominant eye [10].
Visual Evoked Potentials were recorded using RMS-EMG MARK-II machine. Visual stimulus was
presented to the subject 200 times on computer screen at a distance of 100cm, with checker pattern of size 8x8.
The most important step in recording VEP was fixing of electrode. The electrode was fixed as per 10-
20 system which was originally devised for EEG recording. Using the 10-20 system the reference midfrontal
electrode was placed at 30% and recording electrodes at 10% of the whole distance from nasion to occipital
protuberance. Thus reference electrode was placed at 10-13 cm above nasion and recording electrodes at 3-5cm
above the occipital protuberance (inion).
The electrodes are attached to the surface of scalp with conducting paste after cleaning vigorously
keeping skin resistance as low as 5k and these electrodes were connected to electrode box by connecting
wires.
One eye was selected, with other eye closed with mask. The subject was asked to see on the fixation
point on the center of screen, relaxed, blinking minimally and concentrating on the stimulus pattern. The checks
were made to reverse at a rate of 1Hz and 200 responses were recorded. The waveform latency in msec and
amplitude in µvolts were measured inbuilt.
III. Statistical Analysis
Descriptive statistical analysis was carried out on this data in the present study. Results on continuous
measurements were presented as Mean SD (Min-Max) and results on categorical measurements were
presented in Number (%). Significance was assessed at 5 % level of significance. Student t test (two tailed,
dependent) has been used to find the significance of study parameters on continuous scale within each group.
Percentile distribution of latencies and amplitude in dominant and non dominant eye were computed.
3.1. Results
Table 1 provides information about the comparision of eye dominance by Porta & Miles test, where
Right eye dominant were 75% & left eye dominant 25% in both Portas & Miles test. In this study we
encountered no subject with conflicting results from the Portas & Miles test.
Effect Of Ocular Dominance On The Latency And Amplitude Of Visual Evoked Potentials
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Table 2 Shows amplitude of dominant eye with a minimum value of 8.06 µv & a maximum value of
11.50 µv with a mean value of 9.88 + SD of 0.79. Non dominant eye showed a minimum value of 7.57 µv & a
maximum value of 10.89 µv with a mean value of 9.45+ SD of 0.73. (Graph 8)
Table 3 Shows dominant eye latency of N70 with a minimum value of 56.25ms & a maximum value
of 80.60ms with a mean value of 65.27+ SD of 5.67. Dominant eye P100 showed a minimum value of 80.00ms
& a maximum value of 104.38ms with a mean value of 90.73+ SD of 7.34.Dominant eye N155 showed a
minimum value of 143.75ms & a maximum value of 181.25ms with a mean value of 161.47+ SD of 10.20.
Non dominant eye latency N70 showed a minimum value of 58.80ms & a maximum value of 80.60ms
with a mean value of 65.91+ SD of 5.40. Non dominant eye latency P100 showed a minimum value of 80.00ms
& a maximum value of 119.40ms with a mean value of 94.29+ SD of 8.22. Non dominant eye latency N155
showed a minimum value of 123.75ms & a maximum value of 184.38ms with a mean value of 160.60+ SD of
12.30.Also shows the percentile distribution of these measures. (Graph 4)
Table 4 shows the effect of eye dominance on Amplitude is increased in dominant eye which is
statistically significant ( P<0.001) compared to the non-dominant eye .(Graph 3)
The effect of eye dominance on latency of N70 and P100 is decreased in dominant eye which is
statistically significant ( P 0.006 & <0.001 ) compared to the non-dominant eye . (Graph 4&5)
The results of N155 was not statistically significant in the dominant and nondominant eye.(P 0.353 ).(Graph 6)
IV. Tables And Graphs
Table 1:
Comparison of eye dominance by Porta & Miles test.
Eye dominance
Right eye
Left eye
Total
Miles Test
75
25
100
Porta Test
75
25
100
Total
150
50
200
Table 2 : Percentile distribution of amplitude Visual evoked Potentials of µv in dominant and non-dominant eye
in young adults
VEP
Min
Max
SD
Percentile
5th
25th
50th
75th
dominant eye
8.06
11.50
9.88
0.79
8.48
9.42
9.76
10.65
Non dominant
eye
7.57
10.89
9.45
0.73
8.19
9.06
9.43
9.72
Graph 1:
Table 3 :Percentile distribution of latencies of Visual evoked Potentials in dominant and non-dominant eye in
young adults
Latencies
Min
Max
Mean
SD
Percentile
5th
25th
50th
75th
95th
Dominant
eye
N70
56.25
80.60
65.27
5.67
60.00
62.50
63.10
66.30
80.60
P100
80.00
104.38
90.73
7.34
80.00
83.80
91.35
97.88
101.30
N155
143.75
181.25
161.47
10.20
149.40
151.90
162.50
169.40
180.60
non
dominant
eye
N70
58.80
80.60
65.91
5.40
61.36
63.10
63.80
67.30
80.59
P100
80.00
119.40
94.29
8.22
80.00
86.30
95.70
101.30
101.90
N155
123.75
184.38
160.60
12.30
145.66
151.90
158.40
169.40
180.60
Effect Of Ocular Dominance On The Latency And Amplitude Of Visual Evoked Potentials
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Graph 2:
Table 4: Comparison of amplitude and Latency in Dominant and Non-dominant eyes
Dominant eyes
Non-Dominant
eyes
P value
Amplitude(µv)
9.88±0.79
9.45±0.73
<0.001**
N70
65.27±5.67
65.91±5.40
0.006**
P100
90.73±7.34
94.29±8.22
<0.001**
N155
161.47±10.20
160.6±12.3
0.353
Graph 3: Comparison of amplitude in Dominant and Non-dominant eyes
Graph 4: Comparison of N70 latency in Dominant and Non-dominant eyes
Graph 5: Comparison of P100 latency in Dominant and Non-dominant eyes
0
2
4
6
8
10
12
Dominant eyes
Non-Dominant eyes
Amplitude(µv)
52
54
56
58
60
62
64
66
68
70
72
74
Dominant eyes
Non-Dominant eyes
N70
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V. Discussion
Dominance is mainly influenced by genetics and is defined as physiological priority or preference by
one member of any bilateral pair of structures in the body when performing various tasks [12]. The lateralization
in eye function is the result of development of binocular vision, with overlapping of the visual fields of the two
eyes. The resulting physiologic diplopia is suppressed from the non-sighting eye. This is thought to be the
mechanism of development of ocular dominance. The input is favoured from the sighting eye. When a choice is
forced between the two eyes, the vast majority of people choose one eye consistently [8].
Some authors have commented that laterality dominance in terms of eyedness is an obvious
phenomenon, although its functional significance is not clear. Some studies have indicated that 60% of their
sample preferred right eye [14]. In one study, 54 patients with either unilateral ptosis or asymmetrical ptosis
were examined. The right eye was dominant in 33 people and the left in 21people [17]. Ptosis occurred on the
side of the dominant eye in 14 individuals and on the non-dominant side in 40 individuals. The study suggests
that levator muscle tone is influenced by eye dominance when ptosis is present. It may be important to treat first
the non-dominant eye in ptosis , which could look worse than it really is if it affects the dominant eye as a result
of retraction of the contralateral levator muscle [17].
Approximately 2/3 of the population is right eye dominant. In our study, by sighting dominance we
found that 75% were right eye dominant & 25% were left eye dominant, which was consistent with the results
of one more study [14]. In our study no subjects were encountered with conflicting results from the Portas &
Miles test. Sighting dominance is most important in clinical investigations & most clinical phenomenon are
related to this type of dominance in ptosis, cataract, myopia etc [8, 14, 17].
Visual evoked potentials are the electrical potentials evoked in the brain by visual stimuli and measure
the speed of the visual pathways and also the synchronized electrical activity in response to a visual stimulus. In
our study, we have measured the activity of monocular stimulation in normal subjects, and have observed the
differences between the amounts of activity evoked by each eye. These values are compared with sighting eye
dominance (DE&NDE). It was revealed in a research that using positron emission test and VEP, integration of
visual information begins in the fusiform gyrus as soon as 80 to 130 milli seconds after the visual stimulus in a
normal human [15].
In our study the time taken from the stimulus to wave N70 of the visual pathway was shorter in
dominant eye compared to the non dominant eye which is statistically significant. Thus a shorter N70 latency
represents faster visual processing in the dominant eye. In a study it was shown that significant visual
processing occurs within 150 ms after ball release in sports and all the main features of VEP also occurs within
a 150 ms period. A shorter N70 latency therefore represents faster visual processing which is required
immediately following ball release in skilled batsmen and would become more critical with high speed
deliveries [16].
In our study the time taken from the stimulus to wave P100 latency was also faster in dominant eye,
reflecting the activity of visual cortex. In another study it was found that there is a faster P100 latency (~4 ms) in
tennis and squash players compared to rowers and sedentary subjects. They related the faster P100 latency,
which reflects activity of the visual cortex to a tennis player’s ability to rapidly process sensory information
[18]. Data of a study showed that, the mean latency of P100 peak was significantly shorter with stimulation of
the dominant eye and amplitude were higher in the dominant eye, which provides objective
electrophysiological evidence of lateralization in the central nervous system [11].
Effect Of Ocular Dominance On The Latency And Amplitude Of Visual Evoked Potentials
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Another study revealed that the influence of eye dominance scaled by six tests on the parameters (N80,
P100latency and N80-P100 amplitude) of the white-black, green-black, red-black and blue-black pattern visual
evoked potentials, with normal visual acuity. The P100 latency of the white black PVEPS, for both sexes,
significantly shorter in the PVEPs of the dominant eye. The results given were that further electrophysiological
evidence for eye dominance as a lateralized CNS phenomenon is not influenced by colour [19].
In our study the Amplitudes were higher in recordings of V. E. P from dominant eye than from the non-
dominant eye which is statistically significant. This is because of increased electrical activity in the visual
pathway.This is in accordance in a study ,that showed the visual processing during the first 100- 150 ms of the
ball flight with binocular vision facilitates retinal activation in talented cricketers [20]. On the other hand, one
study performed a spectral analysis on steady state V. E. P obtained from dominant and non-dominant eyes
found no difference in power values of VEP [21]. Another study reported that eye dominance of dextrals
appeared to play a role in determining the hemispheric asymmetry [22].
VEP is very important non-invasive tool in detecting abnormalities of visual system & have a wide
range of clinical applications. As technology continues to evolve, VEP will likely provide more qualitative and
quantitative information regarding the function of the optic nerve & kinetics of synaptic plasticity. Study of
normal ocular dominance is amenable for future studies with VEP using variety of stimuli and such
physiological measures are needed to fully understand the functional significance.
It is not only useful for clinical neurophysiologist or ophthalmologist but also for neurologist and
neurosurgeons. Sighting dominance is most important in clinical investigations.
In addition, understanding the extent of eye dominance in normal subjects is important for the study and
interpretation of monocular clinical eye diseases (ptosis, amblyopia, myopia etc.) and also in sports which
require aim (archery, darts or shooting).
VI. Conclusion
In conclusion, 75% of the subjects were right eye dominant and 25% were left eye dominant. The
latency of N70 & P100 has been found to be lesser in the dominant eye and the amplitude is increased in the
dominant eye as compared to non-dominant eye, which provides electrophysiological evidence of lateralization
in the central nervous system.
Acknowledgements
Prof.Ravi.M, Dept of Anaesthesiology for helping in editing and constant support.
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... The present study revealed 69% of the total subjects studied, as right eye dominants and left eye dominant were 29% by subjective tests for eye dominance. In previous studies by Jagdamba et al, 75% were found to be right eye dominants and 25% as left eye dominant candidates, while Thakur et al suggested 2/3 rd of subjects as right eye dominants [21,22]. Among male subjects, 74% revealed right eye dominance while 60% females demonstrated the same in the present study which conforms to the prevalence of preponderance of right eyedness in males as compared to females in the previous studies. ...
... [23] The study demonstrates decreased mean P100 latency and increased mean N75-P100 amplitude in the dominant eyes in both the right eye as well as the left eye dominants with statistical significance. The findings conform to the similar studies in the past.[21][22][23][24][25]In the present study, the latency of P100 wave was shorter in dominant eye, reflecting the faster conduction and activity in the visual cortex. Data of a study showed that the mean latency of P100 peak was significantly shorter with stimulation of the dominant eye and amplitude was higher in the dominant eye, which provides objective electrophysiological evidence of lateralization in the central nervous system. ...
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