Risk Factors for Nearsightedness during early Life, Childhood and Adolescence

Nearsightedness is an essential public health issue that affects people worldwide. Nearsightedness is becoming more common, posing a significant socioeconomic burden. High nearsightedness that worsens over time might result in sight-threatening ocular problems. As a result, it's critical to avoid early-onset nearsightedness from escalating to high pathological nearsightedness. According to recent epidemiological studies, increased outside time is a significant modifiable environmental component that prevents young children against nearsightedness: outdoor light intensity, chromaticity during the day, and Vit. D levels may all play a role in this protective effect. This article summarises the possible protective relation between outdoor duration and nearsightedness. In light of new research, various environmental risk factors like near-work activities, the season of birth, smoking habits in parents, and birth order are also explored. This will allow for the implementation of preventative measures such as health education. Nearsightedness has grown significantly more widespread in recent decades, with certain highly educated groups, like students of law and medical fraternity, having nearsightedness rates of up to 80%. An increase in the number of instances of a high level of nearsightedness has been seen, which corresponds to the growth in nearsightedness. Myopia is said to be caused by multiple etiologies , High nearsightedness in early life is associated with high nearsightedness prevalence later in adulthood. Environmental variables such as greater academic pressure, more desk vocations, and urbanisation may be major drivers in current school nearsightedness trends, as seen by the rapid growth in nearsightedness prevalence observed in several parts of the world. Review Article Sharma and Kher; JPRI, 33(61A): 134-140, 2021; Article no.JPRI.79850 135

Keywords: Vision of children; nearsightedness; risk factors.

INTRODUCTION
Myopia, often known as nearsightedness, is a eye disorder in which the picture is focused before it reaches the retina. The image is not focussed and produced on the retina, therefore it seems blurry to the patient. For a human to visualise any item properly, an image should be focused clearly onto the inner part of the eye i.e. retina. Nearsightedness can be optically corrected with optimally powered glasses or lenses to assist a clear and focused image on the retina [1].
Because nearsightedness is a major reason of vision loss in individuals all across the globe, it is one of the five immediate priorities for the World Health Organization's (WHO) "Vision 2020" campaign [2]. Nearsightedness has grown significantly more widespread in recent decades, with certain highly educated groups, like students of law and medical fraternity, having nearsightedness rates of up to 80% [3]. An increase in the number of instances of high nearsightedness has been seen, which corresponds to the growth in nearsightedness. High nearsightedness is a severe public health concern because it increases the risk of ocular diseases such as myopic retinal degeneration, glaucoma, cataract, visual impairment, blindness, and retinal detachment [4,5]. As a result, it's vital to discover associated risk and preventative variables in development and pathophysiology of near sightedness [6].
Myopia is said to be caused by multiple etiologies [7]. High nearsightedness in early life is associated with high nearsightedness prevalence later in adulthood [8,9]. Environmental variables such as greater scholastic pressure, more desk vocations, and urbanisation may be major drivers in current school nearsightedness trends, as seen by the rapid growth in nearsightedness prevalence observed in several parts of the world [7,10].
Near work includes activities like reading, studying (doing homework, writing), computer use/playing video games, and watching television, to name a few. Because of obvious increased visual demands of close activities like reading and susceptibility of nearsightedness to develop over the schooling age, the amount of time children spend on reading as well as performing other near tasks has already been thought to be a prima facie case of nearsightedness development. However, no consistent connection has been found between reading duration and nearsightedness [11,12,13]. As a result, this research aims to investigate the relationship between nearsighted activities and nearsightedness by examining and synthesizing all relevant and available studies [6].

METHODOLOGY
According to Medline, PubMed and Google Scholar, the risk factors and prevalence of nearsightedness in children were found in studies published till June 2021. Prevalence, incidence, nearsightedness, risk factors, refractive error, and visual impairment were implemented in numerous combinations ("prevalence" [All Feilds] OR "incidence" [All Feilds]) AND ( "risk factors" [All Fields] OR "nearsightedness" [MeSH Terms] OR "visual impairment" [All Fieilds] ). The researchers looked at all English-language articles as well as abstracts from non-English publications. As a prospective source of information, reference lists from pertinent publications were also explored, if they were necessary to make conclusions, other research (e.g., older than 5 years) were included in the discussion section. The study technique and data quality were scrutinized, particularly the definition of nearsightedness and risk factors. There were no attempts to locate previously unpublished information. We looked for studies that looked at any near-work activities with nearsightedness as an end measure, as well as studies that looked at nearsightedness incidence or progression. Studies involving individuals above the age of 18 have been excluded.

DISCUSSION
According to the National Eye Institute, the most common disease diagnosed in children between the ages of 6 to 14, i.e. when they are in school is Nearsightedness. Because eyes are still growing at this age, their shape may vary [14].
The majority of human nearsightedness develops during the time that children attend school in modern civilizations, but Nearsightedness is uncommon among youngsters who do not attend school [15]. This indicates that a school-aged child's nearsightedness develops as a function of their life experiences. Because completely abandoning school or education isn't a feasible option for avoiding potential nearsightedness, the part of the difficulty is to start figuring out the changes that occur in children's lives when they commence school truly help contribute to nearsightedness [16].
Since childhood, if a person has been myopic, they are likely to stay myopic as adults. Another risk factor for nearsightedness is visual stress. This is the result of detailed labour, such as reading or using a computer, causing eye strain. Nearsightedness can also be passed down the generations. If one or both parents are nearsighted, the child's chances of being myopic are six times higher than normal [12].

KEY POINTS
• Nearsightedness commencing school nearsightedness has mostly been seen in the industrialised nations, with just around 1% of the population affected by mostly hereditary types of the condition.
• Both within and between the populations, environmental risk factors have quite a considerable influence on the formation of "school nearsightedness." • The formation of an increased incidence of nearsightedness is mostly due to exposure to environmental risk factors within populations. • Educational constraints, possibly best represented in terms of proximity to employment, and restricted time outdoors during daylight hours are the two primary environmental risk factors found. • These risk factors strongly imply that interventions centered on reducing the quantity of nearsighted work and increasing the amount of time spent outside in school hours are thought to effectively combat the nearsightedness pandemic [17].

AGE
An important predictor of nearsightedness is to have a less hyperopic refraction at an early age [18]. The largest risk factor for progression of nearsightedness is to have a refraction of -1.25 D at an early age. This group have a considerably greater endpoint amount of nearsightedness, but it also has a faster and more effective rate of development and axial length elongation [19]. Although it often makes painfully obvious that a young patient with nearsightedness will also have a greater total of nearsightedness at stabilisation, the cause for the significantly higher rate is unknown. The average age of nearsightedness stability is 15.61 yrs, and the av. level of nearsightedness during stabilisation is 4.87 D, according to the COMET Group. It was also revealed that the total average amount of nearsightedness increased with each year of delayed stabilisation [20].

PARENTAL NEARSIGHTEDNESS
According to research study, even in one parent, parental nearsightedness has been commonly associated with a significantly larger frequency of juvenile nearsightedness. It has also been recently suggested that if both parents are myopic, the likelihood of juvenile-onset nearsightedness is six times higher [21]. In Australia, incidence nearsightedness in 6-yr-olds drastically raised from 7.8 percent with no parental nearsightedness to 21.4 percent and 22.0 percent with one or both parents having nearsightedness, respectively. According to the study, nearsightedness was known to be more common in European Caucasian offspring with myopic parents [22].
Nearsightedness in parents is a risk factor for children to get progressive nearsightedness as well as having nearsightedness themselves. The COMET scientific research, which previously indicated that paternal nearsightedness was connected in some way to myopic advancement and axial length increases, supported this theory [23].

GENDER
The research is inconsistent when it comes to determining sex tendency for nearsightedness. In the COMET study [24], there was no difference between males and females. Women exhibited a significant prevalence of nearsightedness than males in the 20-40yr old groups (39.9 percent and 32.6 percent, respectively, P.001), but this was not fairly constant throughout other age groups, according to the both National Health and Nutrition Examination Survey [25].
According to the COMET study's analysis, men repeatedly exhibited slower progressive rate of nearsightedness than women, confirming prior debate of a more significant overall women incidence of nearsightedness at 20-39 yrs. It's intriguing that there had been nil difference in axial length elongation between men and women. Females had shorter axial lengths as compared to men, however this easily countered by women having steeper corneas [24].

ENVIRONMENTAL FACTORS
Many studies conducted to investigate various environment-related or non-genetic variables may influence the development of nearsightedness. The quantity of close work a kid undertakes during the day, like reading or using hand-held devices, has been found to have a poor or non-existent link [2]. One of the most prevalent and powerful associations is time spent outside. Several studies have shown spending time outside to have a detrimental or protective influence on nearsightedness [22]. In a metaanalysis, Sherwin et al. conducted research and included all of the available research on the connection between outdoor time and nearsightedness in children under the age of 20 [22]. Their findings not only confirmed that spending more time outside lowers the risk of getting nearsightedness, but they also eventually discovered that each additional hour spent outside each week decreased the risk of developing nearsightedness by 2% slightly. As a result, the greater emphasis has changed away from proximity to work and toward the awareness and understanding that time spent outside may have a greater environmental impact. Children who spend more time outside have a decreased risk of acquiring or having nearsightedness. This provides a practical solution to this issue for nearsightedness prevention and the myriad other advantages related to outdoor acts. Although many research & study has gone to the genetics & inheritance of refractive abnormalities, there is still much to learn [21].

ETHNICITY
Ethnicity was previously thoroughly explored as risk factor in progression because of greater prevalence & yearly prevalence rates in Asian individuals [20]. According to the COMET Group study, African-Americans stabilized at younger age (thirteen yrs), with lower nearsightedness (4 Diopteres) at stabilisation. Asians took longest (16 years) for stabilise, whereas the Asians had highest nearsightedness (5.5 D) at final moment of stabilisation, according to the same study [21].

LIGHTING AT NIGHT
Length of the everyday light and dark phases may negatively affect axial length & refractive error progression. Epidemiological studies have had mixed outcomes. According to a survey of 479 children of 2-16 yrs, those who slept under light at night showed a significantly greater risk of developing nearsightedness [22]. Nearsightedness in parents was not considered. The children were selected from a limited cohort. Another research of 77 myopic subjects revealed that those exposed to 5.6 hrs or less of everyday darkness had increased incidence of nearsightedness development than those students who were exposed to >5.6 hrs of everyday darkness. This conclusion was not same in two group-based study of schoolchildren of the US and Singapore. We recommend birth cohort studies of precise refraction and biometry data, as well as extensive assessments of children's nightlight habits before the age of 2 yrs, be conducted [2].

GENE -ENVIRONMENTAL INTERAC-TION
Prevalence of nearsightedness in specific groups such as the Chinese and the Japanese groups implies that genetics have a role, but abrupt shift of incidence rates over the previous-gen also suggests that environment factors play a role too. According to twin studies done in the United Kingdom and Taiwan, Monozygotic twins had a higher concordance rate for nearsightedness than dizygotic twins. On the other hand, heritability is population-specific and varies based on the gene pool. According to his findings, the outcomes of Ashton S9's segregation analysis investigations in Hawaii may be multidimensional. High nearsightedness genetic loci have been discovered (1811.31, 12q 21-23, 7q36), and genome-wide scans to hunt for nearsightedness gene anomalies are being conducted. More research, like family-based association studies and twin studies, might help us better understand how genes and environment interact [26].

CONCLUSION
Finally, the current study's total prevalence of nearsightedness was rather high, showing, nearsightedness is a public health concern among school-aged children. Women, rising age, nearsightedness in parents, spending less time outside, and spending more time inside were all significant factors in nearsightedness. Spending more than 1 hour on electronic devices greatly influenced nearsightedness risk. The pathophysiology of near sightedness is yet unknown. We may infer that nearsightedness is a complex disorder with several causes, including gene, environmental (external), and microenvironmental variables. Despite the fact that nearsightedness has hereditary part, with a variety of genes and putative locus associated to the condition, environmental variables including high education, extended close work, exposure to light & a lack of outdoor activities appear to have a substantial impact. Inflammation and the production of particular proteins connected to alterations in collagen fibres, scleral thinning, and axial length elongation have all been linked to nearsightedness in several studies. We emphasise that the entire mechanism behind aberrant physiological changes in the formation and progression of nearsightedness would be better understood if the investigation was conducted at the cellular and molecular level, following a thorough review of the most current and relevant research. As a result, further investigation is needed. A number of genes and possible loci have been discovered, and as we understand more about the causes of nearsightedness, we may be able to identify potential therapy targets to postpone or prevent the onset of nearsightedness and its effects.

CONSENT
It is not applicable.

ETHICAL APPROVAL
It is not applicable.