Methodological quality of the review: Medium confidence

Author: Brien A. Holden, Timothy R. Fricke, David A. Wilson, Monica Jong, Kovin S. Naidoo, Padmaja Sankaridurg, Tien Y. Wong, Thomas J. Naduvilath, Serge Resnikoff

Region: Worldwide

Sector: Myopia and high myopia

Subsector: Epidemiology of myopia and high myopia

Equity focus: No

Study population: All ages

Type of programme: Global prevalence

Review type: Other review

Quantitative synthesis method: Systematic review and meta-analysis

Qualitative synthesis method: Not applicable

Background: In 2010, it was estimated that uncorrected refractive error was the most common cause of distance vision impairment, affecting 108 million people, and the second most common cause of blindness globally. The economic burden of uncorrected distance refractive error, largely caused by myopia, was estimated to be $202 billion (US dollars) per annum. However, myopia brings further vision challenges because high myopia increases the risk of pathologic ocular changes, such as cataract, glaucoma, retinal detachment and myopic macular degeneration, all of which can cause irreversible vision loss. There remain two major gaps in the literature. However, there are no precise estimates of the global prevalence of myopia or for projected temporal changes over the next few decades.

Objectives: The aim of this study was to estimate the global prevalence of myopia or projected temporal changes over the next few decades.

Main findings: A total of 145 studies covering 2.1 million participants were included in study. Results on the total number of people with myopia globally show that in 2000, this was 1.406 million (22.9% of the global population; uncertainty interval, 932-1932 million [15.2%-31.5%]), increasing to 1.950 million in 2010 (28.3% of the global population; 1422e2543 million [20.6%-36.9%]). This is projected to increase to 2620 million in 2020 (34.0% of the global population; uncertainty interval, 1976-3366 million [26.2%-42.6%]), to 3361 million by 2030 (39.9% of the global population; uncertainty interval, 2578e4217 million [32.3%-47.5%]), to 4089 million by 2040 (45.2% of the global population; uncertainty interval, 3145e5128 million [38.1%-52.1%]), and to 4758 million by 2050 (49.8% of the global population; uncertainty interval, 3620-6056 million [43.4%-55.7%]). Asia-Pacific is the region with a significantly higher prevalence of myopia compared to any other region. Regarding high myopia, this was 163 million in 2000 (2.7% of the global population; uncertainty interval, 86e387 million [1.4%-6.3%]), increasing to 277 million in 2010 (4.0% of the global population; uncertainty interval, 153-589 million [2.2%-8.6%]). This is projected to increase to 399 million in 2020 (5.2% of the global population; uncertainty interval, 233-815 million [3.1%-10.3%]), to 517 million by 2030 (6.1% of the global population; uncertainty interval, 298-1082 million [3.7%-12.2%]), to 696 million by 2040 (7.7% of the global population; uncertainty interval, 381e1518 million [4.6%-15.4%]), and to 938 million by 2050 (9.8% of the global population; uncertainty interval, 479-2105 [5.7%-19.4%]).

Authors conclude that myopia and high myopia estimates from 2000 to 2050 suggest significant increases in prevalence globally, with implications for planning services, including managing and preventing myopia-related ocular complications and vision loss among almost one billion people with high myopia.

Methodology:

Population-based surveys studies were selected for inclusion by authors. A systematic search and review of the prevalence of myopia and high myopia using data published since 1995 was performed. The search was conducted on PubMed (National Library of Medicine) on 10 January 2015, for publications using the following MeSH (Medical Subject Heading) terms: myopia AND prevalence and refractive error AND prevalence. The search was restricted to articles published after 1 January 1995, and was performed on all available articles regardless of the original language of publication. Countries were grouped into the 21 Global Burden of Disease (GBD) regions. The most common definition of myopia was spherical equivalent of -0.50 diopter (D) or less (58.7%), with 29.0% using less than -0.50 D, 5.0% using -1.00 D or less or less than -1.00 D (all studies of adults), 2.9% using -0.75 D or less or less than -0.75 D, and 3.6% using -0.25 D or less or less than -0.25 D. Only 59 studies defined and measured high myopia, with 30.5% defining it as -6.00 D or less, 30.5% defining it as less than -6.00 D, 35.6% defining it as 5.00 D or less or less than 5.00 D, 1.7% defining it as -8.00 D or less, and 1.7% defining it as -3.00 D or less. Analysis: A meta-analysis of the prevalence of myopia and high myopia within each age group of each GBD region, using the standardised myopia definitions and a standardised time point of 2010, was performed using Comprehensive Meta-Analysis software version 3 (Biostat, Englewood, NJ). A logit random effects model was used to combine studies within each age group and region. The logit prevalence was defined as log (P/(1 E P)), where P is the prevalence within each age group. The study-to-study variance (s2) was not assumed to be the same for all age groups within the region, indicating that this value was computed within age groups and was not pooled across age groups. The inverse of the variance was used to compute relative weights. The logit prevalence and its standard error were used to compute the 95% confidence limits, which was then transformed to the estimated prevalence and its corresponding limits using the formula E ˇ(logit prevalence)/(Eˇ(logit prevalence) þ 1), where E ¼ Euler’s number.

Applicability/external validity: This review was conducted worldwide with inclusion of studies from LMIC. The results can be applied worldwide. The authors further added that myopia and high myopia changes seen in African Americans were very similar to those in European Americans.

Geographic focus: Worldwide study.

Summary of quality assessment:

Medium confidence was attributed to the conclusions about the effects of this study. Contacting authors/experts were not part of the search strategy, and inclusion of studies was restricted to those published after 1995. Authors did not report methods used to assess the quality of included studies and methods to screen studies for inclusion and the extraction of data of included studies.