Natl. J. Physiol. Pharm. Pharmacol. (2025), Vol. 15(2): 193-196

Original Research

10.5455/NJPPP.2025.v15.i2.13

Visually evoked potential waves in medical students with myopia using smartphones

Rozy Paul¹*, RajPrabha², Madhvika Shah² and Minal Kachhawa²

¹Department of Physiology, MGMCH Jaipur, Jaipur, India²Department of Physiology, RUHS College of Medical Sciences, Jaipur, India

*Corresponding Author: Rozy Paul. Department of Physiology, MGMCH Jaipur, Jaipur, India. Email: rozy747 [at] yahoo.co.in

Submitted: 16/09/2024 Accepted: 16/01/2025 Published: 28/02/2025

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Abstract

Background: Visually evoked potential (VEP) is principally used to evaluate the functional cohesion of visual pathways. Refractive errors deform the stimuli, causing loss of focus and affecting the VEP variables. There is a strong rationale for estimating the dangerous effects of Electromagnetic Radiation waves produced by smart mobile phones on the human visual system.

Aim: To study the visually evoked potential waves in myopic medical students using smart mobile phones for more than 3 hours/day and to compare them with normal healthy controls.

Methods: This analytical study was conducted in the Department of Physiology of a tertiary care teaching institute from July 2023 to September 2023. A total of 60 MBBS students were studied; 30 myopic students using smart mobile phones for more than 3 hours/day. The control group included 30 students with normal vision using a smartphone for more than 3 hours/day.VEP was performed. The statistical analysis of data was done with a student-independent unpaired “t” test using SPSS 23.0.

Results: There was a significant increase in the latencies of P100 and N135 in individuals with myopia using smart mobile phones for more than 3 hours/day compared with the controls for both the right and left eyes. The latencies of N75 in individuals with myopia were increased but statistically insignificant for both the right and left eyes.

Conclusion: Myopia, if not corrected, in students using smart mobile phones for >3 hours/day, can lead to significant prolongation of VEP latencies.

Keywords: Mobile phone, Myopia, Refractory errors, Visual Evoked Potential.

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Introduction

According to the National Programme for Control of Blindness, uncorrected refractive errors are the second most common (19.7%) cause of avoidable blindness in India (National Programme for Control of Blindness (NPCB) 2010). A myopic person is not able to focus on distant objects with a sharp focus on the retina. However, as an object shifts closer to the person’s eye, it becomes focused on the retina. When the object comes closer to the eye, the person accommodates(accommodation reflex) to keep the image clearly focused (Holden et al. 2017).

The visual evoked potential (VEP) is a graphical representation of cerebral electric potentials originating from the visual cortex in response to a defined visual stimulus (Kothari et al. 2014). Electrical potentials are recorded from the scalp overlying the occipital cortex. The VEP waveforms a type of electroencephalogram wave signal. VEP is principally used to inspect the functional unity of the afferent visual pathways originating from the retina through the optic nerves to the occipital cortex of the brain (Kothari et al. 2014). VEP is one of the most important clinical devices developed from neurophysiological research. Any irregularity that affects the visual pathways or visual cortex in the brain can disturb the VEP as in cortical blindness (Kothari et al. 2014).

The close approximation of eyes, including visual pathways to mobile phone antennas during phone calls exposes these tissues to excessive electromagnetic radiation (EMR). Therefore, there is a strong rationale for determining the deleterious effects of electromagnetic waves generated from mobile phones on the human visual system (Switzer and Mitchell 1977; Vignal et al. 2009). Blue light has a greater tendency to affect human eyes by disrupting biological processes that rely on natural day and night cycles. Therefore, light emitted by smart mobile devices that are of short wavelength (blue) should be avoided during nocturnal hours as it can lead to deleterious effects (Kaushik and Singh 2016). Since there has been extensive research on the effect of myopia and usage of mobile phones on VEP separately, this study provides the outcome of mobile use in myopic subjects on VEP (Kaushik and Singh 2016). This study aimed to compare and assess the latency and amplitude of N75, P100, and N135 waveforms in subjects with myopia using smart mobile phones for more than 3 hours/day with normal healthy controls using smartphones for less than 3 hours/day.

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Materials and Methods

This analytical study was conducted in the Department of Physiology of a tertiary care teaching institute from July 2023 to September 2023. All subjects were clinically examined for myopia diagnosis. The visual acuity test was performed for near vision by Jaeger chart; and for distant vision by Snellen’s chart. A color vision test was performed using Ishihara chart. An elaborate past history was recorded, and a physical examination was performed. A total of 60 MBBS students were finally selected and studied; 30 students with myopia using smart mobile phones for more than 3 hours/day (at least 1 year) were included in the case group, and 30 students with normal vision using smartphones less than 3 hours/day (at least 1 year) were included as the control group.

Inclusion Criteria: (a) age: 18–35 years, (b) both genders, and (c) refractive error (myopia), subjects with normal vision (controls).

Exclusion criteria

Age <18 years and >35 years, (b) other refractive errors (hypermetropia, astigmatism), (c) history of color blindness, glaucoma, cataract, optic neuritis, and any other eye pathology, (d) history of seizures, eye surgery, demyelinating diseases, diabetes mellitus, hypertension, thyroid abnormalities, known smokers, alcoholics, tobacco chewers, and (e) subjects on barbiturates, neuroleptics, and antidepressants.

VEP was performed as per the inclusion and exclusion criteria for cases and controls, and the latency of all three waves (75, P100, and N 135) was recorded. The control group consisted of 30 age-matched normal subjects. The association between the duration of smart mobile phone usage and the duration of mobile phone use was evaluated using a questionnaire asking about the duration of mobile phone use in a day (less than 3 hours per day of mobile screen time or more than 3 hours of screen time), the usage of a smart mobile phone in the day or night time.

Technique

VEP was recorded by NEUROPERFECT EMG 2000. VEP was recorded by placing three electrodes (active, reference, and ground) in three different locations on the subject. (a) The active electrode (Oz) was placed 3 cm above the inion, (b) the reference electrode (Fz) was placed 12 cm above the inion, and (c) the ground electrode (Cz) was placed over the forehead(Kothari et al. 2013; Kaushik and Singh 2016).

Written informed consent was obtained from the participants after explaining the study plan and procedures. Subjects were asked to sit on a table in a relaxed position about 100 cm from the monitor. The visual stimuli consist of a black and white chessboard pattern generated on a TV system reversing at the rate of 1.5Hz is shown to one eye, whereas the other eye is being covered. Subjects were instructed to concentrate on a rectangle shown at the center of the screen. A total of 100 stimulations were presented monocularly. The signals detected by the electrodes were filtered, amplified, averaged, and finally displayed on the TVscreen. The normal VEP recording was composed of 3 waves, i.e., N75, P100, and N135 waves. The latencies of waves N75, P100, and N135 were recorded.

Data acquisition and analysis

All data were entered into an MS Excel spreadsheet. The data were expressed as mean ± standard deviation, and descriptive tables were generated. The data were then statistically analyzed using Student’s independent unpaired sample “t” test. The statistical analysis was performed using a statistical package for social sciences (SPSS version 23.0 for Windows 10).

Ethical approval

The ethical clearance of the study was obtained from the Institutional Ethical Committee (IECNo: RUHS-CMS/ Ethics Comm./2023/215,13/09/2023).

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Results

Each group contained 30 cases and 30 controls, as shown in Table 1. The age of the participants ranged from 18 to 24 years. The primary variables of age, height, and weight were matched between the controls and cases (p > 0.05).

There was a highly significant increase in the latencies of P100 in individuals with myopia using smart mobile phones for more than 3 hour/day compared with controls for both the right eye (p=0.0005) and left eye (p < 0.05). The latencies of N135 were significantly increased in the left eye (p=0.001) but increased not significantly (p=0.181) in the right eye in cases compared with controls. The latencies of N75 in individuals with myopia compared with the controls for both the right (p=0.50) and left eye (p=0.232) were increased but not statistically significant (Table 1).

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Discussion

Uncorrected refractive errors area leading cause of visual disability. Myopia or “near sightedness,” is defined as a type of refractive error in which parallel rays of light coming from infinity are focused in front of the light-sensitive retinal layers when the ciliary muscle is completely relaxed (eyes in the position of rest) (Odom et al. 2004). The eye is considered normal when parallel light rays from an object at a distant location are in sharp focus on the retina and the ciliary muscle is completely relaxed. This means that the normal eye with a relaxed ciliary muscle can clearly see all distant objects clearly (Odom et al. 2004).

A myopic person has a definite limiting “far point” for clear vision (Holden et al. 2017). This condition is usually due to the elongation of the eyeball and can also result from excessive refractive power in the lens system of the eye. There is no mechanism by which the strength of the eye lens decreases to less than the strength of the eye that exists when the ciliary muscle is completely relaxed (Holden et al. 2017).

Table 1. Comparison of VEP parameters between controls and cases.

VEP greatly emphasized the fovea centralis region and was more sensitive to small refractory changes than electroretinogram (Kothari et al. 2014). Any irregularity that affects the visual pathways or visual cortex in the brain can disturb the VEP, as in cortical blindness due to meningitis or hypoxia, optic neuritis as a consequence of demyelination, optic atrophy, stroke, and compression of the optic pathways by certain tumors, hydrocephalus, amblyopia, and neurofibromatosis (Creel 1995).

Mobile phones are widely used as telecommunication and learning devices. According to recent statistics, global smart mobile phone penetration was 69%, and worldwide smart mobile phone subscriptions have reached 6.7 billion people (Federica Laricchia). The use of smartphones has considerably increased the daily EMR exposure. The eyes, including visual pathways, are near the smartphone antenna during a phone call. Eye tissues are more susceptible to the heating effects of EMR and damage due to the presence of fewer blood vessels as compared to other organs (Vignal et al. 2009). There are concerns that the EMR emitted from smartmobile phones has a deleterious effect on the human visual system (National Programme for Control of Blindness (NPCB) 2010).

In our study, the latency of all three waves (N75, P100, and N135) was longer in cases than in controls in the right eye as well as the left eye. The change was highly significant, statistically (p value < 0.01) for wave P100 (clinically the most useful parameter. The latency and shape of P100 depend on the fibers that survive the fastest. This finding was in accordance with a preceding study, in which it was accepted that myopia and hyperopia with and without correction of refractive error markedly increased the latency of P100 and reduced the amplitude (Kothari et al. 2013).

A previous study assessed the P100 latency in myopia and established that there is a significant inverse association between refraction and P100 latency (Lee et al. 2002). It was found that the P100 latency was extremely long, and a significant difference also existed in relation to amplitude between the myopic and control subjects (Vinodha and Shanugapriya 2005). VEP was considered by taking the whole-field pattern reversal chessboard pattern as the stimuli, and the refractive impairment was measured. The statistical results revealed prolonged P100 latency in myopic subjects along with significant decreases in P100 amplitude.

One study observed that VEP amplitude decreased by approximately 25% per diopter defocus, and the effect was recognizable for 0.25 dioptres (Ludlam and Meyers 1972). A recent study found that induced myopia and hypermetropia were strongly correlated with P100 L (length) and P100 A (amplitude). P100 A progressively decreased and P100 L progressively increased with an increase in both induced myopia and hypermetropia (Anand et al. 2011). Additionally, there is a definite gender difference in VEP parameters, with females showing shorter P100 latency and higher amplitude (Sharma et al. 2015; Gupta et al. 2021). The commonest cause of prolonged P100 latency is demyelination in the optic pathways (Reimslag et al. 1985). Switzer and Mitchell reported an increase in the myelin degeneration of neurons in the brain of rats at 6 weeks after repeated exposure to continuous EMR wave (Switzer and Mitchell 1977). The long-term effects of smart mobile phones, especially in patients with myopia should be done to further evaluate its adverse effects and thwart necessary measures to prevent further morbidity.

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Conclusion

Uncorrected myopia in students using smart mobile phones for >3 hour/day causes prolongation of VEP latencies. Electromagnetic radiation emitted by smart mobile phones affects the visual system, especially visual pathways. The changes are cumulative, as evidenced by the longer latency and smaller amplitude of mobile phones used for longer periods.

Limitations

Small sample size and absence of long-term follow-up.

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