A systematic review of near work and myopia: measurement, relationships, mechanisms and clinical corollaries.

Author: Gajjar S, Ostrin LA.

Geographical coverage: Worldwide

Sector: Biomedical

Sub-sector: Risk

Equity focus: None

Study population: People with myopia

Review type: Other review

Quantitative synthesis method: Systematic review

Qualitative synthesis method: Not applicable

Background: Accumulating evidence suggests that behavioural and environmental factors play a major role in eye growth and myopia development. Time outdoors, near work, education and urbanisation are all potential influences for myopia onset and progression. Controversy remains as to how much, if at all, each of these factors contributes to myopia. After decades of investigation, the role of near work in myopia remains unresolved, with some studies reporting no relationship and others finding the opposite.

Objectives: To summarise classic and recent literature investigating near work and the onset and progression of myopia, potential mechanisms, and pertinent clinical recommendations.

Main findings:

In summary, the researchers discovered that while the existing literature presents mixed findings, a significant number of studies do indicate a correlation between near work and myopia.

A multitude of cross-sectional studies included in this review have reported an increased likelihood of myopia with more near work, as per the researchers. Although initial longitudinal studies did not identify this correlation, more recent ones have established a link between myopia and near work. The focus has shifted from the daily duration of near work to the absolute working distance and the length of uninterrupted near viewing. A few studies have identified that shorter working distances and continuous near viewing for more than 30 minutes are risk factors for the onset and progression of myopia. To better investigate these aspects, new devices that can continuously measure range have been developed. The conflicting nature of the literature is likely due to the subjective and variable ways in which near work has been quantified, coupled with a lack of longitudinal studies.

Recent research suggests that the impact of near work on the onset and progression of myopia may be associated with the characteristics of near work, specifically, absolute working distances and temporal properties. Authors report that a better understanding of the roles of absolute working distance, temporal properties, viewing breaks and electronic device use on myopia development and progression will aid in the development of evidence-based clinical recommendations for behavioural modifications to prevent and slow myopia.

Study authors note the need of more precise objective measures of near viewing behaviour to make definitive conclusions regarding the relationship between myopia and near work. The focus should shift to utilising objective and continuously measuring instruments to quantify near-work behaviours in children, followed longitudinally, to understand the complex factors related to near work.

Methodology:

Studies were chosen for inclusion using the Joanna Briggs Institute checklist, with a focus on studies with a sample size greater than 50. Further inclusion criteria were not clearly stated.

The authors utilised PubMed and Medline to locate peer-reviewed cross-sectional and longitudinal studies that explored the relationship between near work and myopia from 1980 to July 2020, adhering to the PRISMA checklist. The search was conducted using the following keywords: “myopia”, “schoolchildren”, “prevalence”, “refractive error”, “risk factors”, “near work”, “screen time”, “electronic device use”, and “accommodation”. In addition to these sources, the reference lists of pertinent publications were also examined to identify any additional articles. The review process followed the guidelines of the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) checklist. Articles were critically reviewed and independently evaluated by the authors, and conclusions were drawn as per these evaluations. Odds ratio for myopia with near work was provided when available, and limitations were considered.

Applicability/external validity: The authors of the review acknowledge several limitations that may affect the validity and applicability of their findings. The review aimed to include as many studies as possible for a comprehensive understanding of the topic, which led to a more lenient inclusion criteria compared to previous meta-analyses. This approach, however, resulted in the exclusion of some important cross-sectional and longitudinal studies. The selection of studies considered various factors such as the impact factor of the journal, the authors of the review, the methodology, and the number of subjects. Despite the extensive coverage of the topic of near work, the review does not claim to provide a complete analysis. Direct comparisons were inevitably subjective and constrained by the use of different metrics and formulas across studies to calculate near-work risk. While a meta-analysis provides objective data analysis and equal synthesis of studies, it typically uses strict inclusion criteria and may not represent all studies. On the other hand, a systematic review, which may include more studies, relies heavily on the authors to synthesize data and draw conclusions, potentially introducing inherent biases and predispositions, even if they are consciously suppressed.

Geographic focus: The review does not specifically mention its geographic focus, however, it evidently includes studies from countries with high, medium, and low income levels.

Summary of quality assessment:

The review provided minimal details about the methodologies employed to identify, select, and critically evaluate the studies. There was no mention of an independent assessment of the included studies by two authors, nor was there any evaluation of the potential bias in individual studies. Furthermore, the review did not make an effort to include unpublished studies or those published in languages other than English. The analysis did not account for the heterogeneity of the included studies or consider their individual quality. Due to these reasons, our confidence in the review’s findings is low.