Changes in Accommodation and Vergence Measurements After Smartphone Use in Healthy Young Adults

Introduction

According to demographic projections, India is expected to reach 442 million mobile phone users by 2022. The largest number of smartphone users are concentrated in India, China, and the United States, with each country surpassing 100 million users.¹ Changes in several ocular functions, such as amplitude of accommodation, accommodative facility, vergence facility, accommodative convergence, and accommodation ratio (AC/A), have been reported in connection to the prolonged use of mobile devices,^2,3 as well as a shorter working distance.^4,5 With the continuous increase in number of smartphone users experiencing ocular or visual problems, the incidence of ocular or visual disorders has also risen. Accommodation has been identified as a significant factor in the symptoms associated with computer usage, which are likely to be observed after prolonged usage of smartphones. Accommodation is the mechanism by which the eye adjusts its focus from far to near objects, achieved by altering the shape of the lens through the action of the ciliary muscle on the zonular fibers. Vergence pertains to the synchronized motion of both eyes in opposing directions, aimed at attaining or upholding a singular binocular vision. When a person possessing binocular vision focuses on an object, the eyes need to pivot around a horizontal axis, ensuring that the image is accurately cast onto the central portion of the retina in each eye.⁷ The aim of this study was to investigate the changes in accommodation and vergence parameters among individuals using smartphones for extended periods. It was essential to determine whether prolonged smartphone use has any adverse effects on ocular health, particularly with regards to accommodation and vergence functions. Therefore, this study will aid in increasing public awareness and understanding of the symptoms and ocular disorders associated with prolonged smartphone use.

Materials and Methods

The present prospective cross-sectional research design study received ethical approval from the Institutional Ethical Committee before being implemented. It was conducted over a four-month period from September to December 2021, at Mangala College of Allied Health Sciences, and recruited college students aged between 18 and 25 years enrolled in an educational program.

The study recruited participants in the age range of 18 to 25 years, who were asymptomatic and had normal vision. The individuals voluntarily participated in the study, and only those meeting the inclusion criteria were selected. Those with any ocular disease or concurrent systemic illness were excluded from the study.

Statistical Analysis

The study utilized descriptive statistics, specifically Mean and Standard Deviation, to analyze the quantitative variables. To compare pre- and post-quantitative variables, a paired t-test was conducted. The statistical analysis was performed using both Microsoft Excel and SPSS 16.0 software versions.

Method

All participants underwent a comprehensive eye examination that included testing of visual acuity for distance and near using the Snellen acuity chart, as well as a slit lamp bio-microscope examination.

The study enrolled only participants with a maximum attainable visual clarity (BCVA) of 6/6 and N6. Near Point of Accommodation and Near Point of Convergence were assessed utilizing a Royal Air Force (RAF) ruler, whereas the measurements for Negative and Positive Fusional Vergence Amplitudes (NFV, PFV) were conducted employing a horizontal prism bar. Accommodative facility (AF) was measured using accommodative flippers, and vergence facility was measured using vergence flippers. Negative relative accommodation (NRA) was assessed by adding plus lenses, and Positive relative accommodation (PRA) was assessed by adding minus lenses binocularly. The Heterophoria method was used to measure the AC/A ratio, and dynamic retinoscopy was employed to assess accommodative responses (MEM). After the initial measurements, the participants in our study were seated comfortably in a normal light-room, without any glare from windows. A reading material was presented to them through a smartphone, featuring black text exhibited against a white backdrop. The font size was N8, and the smartphone had a 5-inch LCD screen with a resolution of 720x1280 pixels. The phone was kept 40 cm away from the eye level, and the auto-brightness feature was used to adjust the screen's luminance based on the normal room illumination. The investigators monitored the distance between the smartphone and the participant's eyes regularly. After engaging in the activity, the participants vocalized the text for a duration of 30 minutes. Subsequent to finishing the task, their visual acuity, accommodation, and vergence measurements were reassessed within a span of five minutes.

Results

The current investigation comprised of 32 individuals, with an average age of 19.00±1.21 years (range: 18-25 years), among whom 12 (37%) were males and 20 (63%) were females. Accommodation and vergence parameters were analysed and the results are presented in Tables 1 and 2, respectively.

Accommodative Measurement

Near point accommodation (NPA)

The study found that the average and standard deviation NPA before the task was 8.42±0.67, and after the task was 9.4±0.74. NPA decreased significantly (p <0.05) which indicates a significant reduction in accommodative power following continuous smartphone use.

Accommodative response (MEM)

The study found that the average and standard deviation accommodative response was 0.67±0.18 before the smartphone task and significantly increased to 1.24±0.31 after the task (p <0.05), indicating an increase in accommodative effort following prolonged smart-phone use.

Accommodative facility (AF)

The average and standard deviation accommodative facility (AF) before the task was 10.95±0.98 cycles per minute (cpm), while after the task, it decreased to 9.01±1.3 cpm (p <0.05). This suggests that prolonged smartphone use for reading leads to a significant increase in accommodative fatigue.

Negative relative accommodation (NRA)

The average and standard deviation of NRA values for the pre-task and post-task measures were 2.28±0.273 and 2.95±0.27, respectively (p <0.05). This indicates that prolonged smartphone use can cause a significant increase in negative relative accommodation.

Positive relative accommodation (PRA)

The study found that the average and standard deviation PRA values before and after the task were 2.87±0.38 and 3.64±0.2, respectively (p <0.05). This indicates that prolonged smartphone use can cause a significant increase in positive relative accommodation.

AC/ A Ratio

The average and standard deviation AC/A ratio values before and after the task were 5.94±0.56 and 6.41±0.79, respectively (p >0.05).

Vergence Measurement

Near point of convergence (NPC)

The average and standard deviation of the NPC values before and after the task were 6.97±0.88 and 9.41±1.28, respectively (p <0.05).

Negative fusional vergence (NFV) and Positive fusional vergence (PFV)

The average and standard deviation PFV at near before and after the task were 13.37±1.87 and 15.18±1.51 (p <0.05), respectively, which indicated a significant increase in the break response.

The average and standard deviation NFV at near before and after the task were 9.68±1.97 and 8.81±1.63 (p <0.05), respectively, which showed a decrease in the recovery response which was significant.

The average and standard deviation of NFV were 9.31±1.4 and 8.1±1.856 for pre and post distance, respectively, and the difference was statistically significant (p <0.05). This indicates a significant recovery response.

Vergence facility (VF)

The average and standard deviation of vergence facility were 9.71±1.61 and 7.1±1.21 cpm for before and after measurements, respectively, with a statistically significant difference of p <0.05. This finding suggests a decline in the ability to rapidly induce and relax convergence after reading on a smartphone.

Discussion

This study sought to describe the comprehensive explanation of accommodative and vergence components that occur after 30 minutes of using a smartphone device. Recent study found that reading text on a smartphone for 30 minutes had a significant impact on the accommodative and vergence components of near tasks.⁸

According to recent literature, the luminance for the participants was adjusted to be constant and equal to 12.8 cd/m².⁸ Whereas in our study, auto-brightness feature was used to adjust the screen's luminance based on the normal room illumination.

Accommodation components

The present study found significant results in the NPA for both the eyes. However, after 30 minutes, there was a decrease in the amplitude of accommodation.^9-11 This reduction in the amplitude of accommodation after 30 minutes is likely attributed to the tonic accommodation generated by prolonged periods of close work.^12,13 The research indicated that the utilization of a smartphone resulted in notable alterations in both negative relative accommodation (NRA) and positive relative accommodation (PRA). These measures of accommodation depend on the coordination of fusional vergence to maintain binocular vision. Therefore, the reduction in fusional vergence may be a probable factor contributing to the observed decrease in relative accommodation.¹¹ The working distance and luminance were continuously monitored, and the text size was set to N8. It was observed that the combination of small text size and prolonged reading without taking breaks could potentially strain the accommodative system, leading to accommodation lag. Furthermore, the changes in accommodative response were found to be related to age and the amplitude of accommodation.¹⁴ The research noted a noteworthy decline in binocular accommodative facility subsequent to smartphone usage.¹¹ In healthy young adults, the AC/A ratio is influenced by the dynamic interplay between accommodation and convergence. The absence of a significant change in the AC/A ratio following monitored reading suggests that these active processes remain stable during this task.¹⁵

Vergence measurement

When doing near visual tasks, a decrease in NPC may cause visual and ocular discomfort.⁸ The present study identified noteworthy alterations in the Near Point of Convergence (break), despite the consistent maintenance and measurement of a fixed working distance over a 30-minute period. After 30 minutes of reading, indirect measures of vergence characteristics such as NRA and PRA dramatically decreased. This demonstrates that extended work duration can cause changes in vergence, raising the probability of ocular tiredness. This is consistent with previous research.^8,9 As the amount of near work increases, patients may begin to experience symptoms that lead to a decrease in visual demand, cognition, and perception. In addition, the study found substantial changes in PFV at near break point and NFV at the near recovery point and distance recovery point during smartphone reading, suggesting a decline in fusional and accommodative vergence.9 Therefore, it is necessary for patients to have sufficient reserve in both vergence and accommodative systems in order to restore binocularity after prolonged smartphone reading. The study's vergence facility showed a significant decrease after the task, indicating that abrupt changes in vergence dynamics cannot be sustained following extended smartphone use.

Conclusion

Following a thirty-minute session of reading text on a smartphone, a notable influence was observed on the accommodative and vergence aspects pertinent to closerange tasks. This resulted in a decrease in the efficacy of both the accommodation and vergence mechanisms. Exposure to these devices can cause eye strain, headaches, and binocular vision problems in young individuals at an early age. Hence, it is advisable to incorporate regular pauses when reading from mobile devices and adhere to the 20-20-20 guidelines during digital device usage. This approach entails taking breaks every 20 minutes to focus on an object positioned 20 feet away for a period of 20 seconds.

Funding

Nil

Conflict of Interest

The authors declared that they do not have any conflicts of interest and hold themselves accountable for the content presented in the article.

Acknowledgment

I would like to convey my sincere appreciation to Prof. Dr. Ganapathi P, the Medical Director of Mangala Group of Educational Institutions, and Prof. Pratijna Suhasini GR, the Dean of Mangala Group of Educational Institutions, as well as my friend Mr. Ragukumar Venugopal, a Research Associate at LV Prasad Eye Institute, and all of my lecturers who have provided me with constant support and encouragement during my academic journey. Moreover, I am grateful to all the study participants for their valuable contribution to this research.