Study of Risk Factors Associated with Myopia in Medical Students: A Case-Control Study

Background: Myopia has emerged as a serious vision-threatening disease globally. Due to its increasing prevalence in the last few decades, it is now considered that along with genetics, environmental and lifestyle factors are also playing some role in the development of myopia. Thus, this study was planned to evaluate the effects of various risk factors in the development and progression of myopia by comparing them with people


Introduction
Myopia is a global public health problem leading to visual impairment and blinding complications. 1 Myopia is the most common ophthalmic condition globally, with an estimated 22.9% of the world population being affected. 2 Although genetic factors play a role in the development of myopia, the rapid rise in prevalence is likely attributable to environmental and lifestyle factors. 3 Prior studies have demonstrated an association between myopia and near-work activities such as studying, reading, and screen time among children. 3,4 A study conducted in Ireland showed that myopia is significantly prevalent among children aged 12 to 13 years, with screen exposure time >3 hours/day, sedentary lifestyle, frequent reading/writing, and less light exposure. 5 A survey conducted in Scotland showed that variable sleep duration and short sleep latency are positively associated with myopia. 6 Another study conducted on Chinese children showed that sleep duration and bedtime are not associated with either progression of myopia or axial elongation. 7 A study conducted in Australia showed that lower daily light exposure is significantly associated with myopia, while physical activity does not show any association with it. 8 Myopics carry higher risks of important causes of ocular morbidity, including retinal detachment, glaucoma, myopic macular degeneration, and cataracts. 9 Parental myopia has a significant positive association with a child having a risk of developing myopia. 10 Little work is done on the effects of lifestyle on myopia in our population. By having deep insight into various factors associated positively with the onset and progression of myopia, we will be able to bring about various preventive methods or lifestyle modifications and thereby contribute to reducing the incidence or progression of myopia. Hence the objective of this study is to evaluate the effects of different risk factors in the development and progression of myopia by comparing them with people without myopia.

Materials and Methods
A case-control study was conducted on medical students from a public medical institution in Rawalpindi from May to September 2019 after obtaining ethical approval from the Institutional Research Forum. Data were collected from 330 medical students through non-probability sampling by using a self-designed questionnaire. Students from all five years of MBBS were included in this study after obtaining informed consent from them. Those with vision defects other than or along with myopia, such as keratoconus, hypermetropia, cataracts, amblyopia, or any other medical or surgical pathology suspected of affecting the vision, were excluded from the study. Participants were divided into two groups based on whether they were myopics (case) or non-myopics (control). Myopics or cases included those who wear spectacles or contact lens and were diagnosed by a certified ophthalmologist. Whereas control included students without any visual defect. Both myopic and non-myopic students included in the study were 18 to 25 years of age. A research questionnaire was developed after an extensive literature review related to risk factors and predictors of myopia. Risk factors include a family history of myopia, sleeping hours at night, screen exposure time, physical activity, study hours and breaks during the study. The questionnaire included different questions on patient demographic details, myopia progression, study and sleep routine, and outdoor physical activity. The questionnaire was disseminated online and in-hand to medical students. The anonymity of participants was ensured and they were voluntarily asked to participate in the study. Data were entered and analyzed using the Statistical Package for the Social Sciences (SPSS), version 25. Descriptive statistics, non-parametric tests, and odds ratio were used to analyze the data. A probability value of less than 0.05 was considered statistically significant.

Results
Out of 330 participants, 185 (56%) were myopics, and 145 (43.9%) were non-myopics. Participants were 18 to 25 years old, having a mean age of 20.87±1.42 years. About 52.5% of myopics had a family history of myopia. Males were less likely to develop myopia than females (OR=0.65). Details about case and control with respect to gender are mentioned in Table-I  during 20 to 25 years, and only 7% observed it when they were less than ten years old. There was no statistically significant difference between cases and controls on the basis of sleeping hours, screen exposure time, study hours and break during the study, indicating no role played by them in developing myopia. Further details are shown in Table-II. The role of physical activity in the development of myopia was also studied by comparing daily hours of physical activity (walk, workout, outdoor sports, etc.) in cases and controls. It was seen that 83.7% of myopics were engaged in physical activity for up to 2 hours/day, while 89.6% of non-myopics spent their 2 hours daily in any sort of physical activity. Further details regarding physical activity are shown in Table-III. Non-myopics were significantly more physically active than myopics (p-value=0.025), showing that low physical activity is associated with the development of myopia.

Discussion
The knowledge and awareness of myopia are very crucial, especially for a developing country like Pakistan, where myopia affects 36.5% of the population and 11.5% of blindness is attributed to it. 11 The development and progression of myopia depend on various factors, including genetics and the daily lifestyle of a person. The results that our study has generated is consistent with other literature studies relevant to risk factors that develop myopia over a long period of time.
The current study suggests that the amount of time medical students spend in near work (reading, screen exposure time) is unlikely to have any meaningful effect on the development of myopia. This could be explained by a 23-year follow-up study conducted in Finland, which states that the time spent on close work and study affected the progression of myopia in children but not in adults. 12 Thus, our study showed no significant differences in cases and controls on the basis of myopia.
A study conducted on older adults in China stated a significant association between the prevalence of myopia and sleep during nighttime. 13 However, our study did not show any significant differences between cases and controls on the basis of sleep routine. Similar results are shown by another study on Chinese children, according to which bedtime and sleep duration have no significant effect on the progression of myopia. 14 This study shows that non-myopic were more physically active than myopics stating that low physical activity might play some role in developing myopia. An inverse interrelation between time spent outdoors (pertaining to physical activities) and incident myopia diagnosed during childhood was evaluated in a clinical study highlighting the importance of physical activity as an essential predictor of myopia progression. 15 Another study aims to reassure the significance of outdoor activities (sport and leisure activities) in protecting against myopia, whereas indoor activities did not affect myopic progression. 16 The possible explanation for this is given by Yuval Cohen, Edna Peleg, et al., who hypothesized that light stimulates the release of dopamine, which antagonizes myopia development. This experiment was conducted on six illumination groups of newly hatched chicks based on exposure to varying intensities of light. 17 This has been supported by several studies that show outdoor activity inhibits myopia, potentially through dopamine-mediated mechanisms. 18,19 Limitations of our study are that convenience sampling made it difficult to generalize our results, especially those parameters (screen exposure time, near work time) for which no significant relation could be drawn but exists as based on previous clinical literature. There is a strong need to conduct similar surveys, preferably in other communities and age groups, as conclusions based on our study are impossible to generalize over the entire myopic population of our country but can help highlight the lifestyle modifications associated with myopia.

Conclusion
There is no significant effect of sleeping hours, screen exposure time, study hours, or breaks during the study on myopia as both myopic and non-myopic medical students have similar habits. Myopia is more prevalent in females, people with a family history of myopia, and those with little physical activity.