The complications of myopia: a review and meta-analysis

Authors: Haarman AEG, Enthoven CA, Tideman JWL, Tedja MS, Verhoeven VJM, Klaver CCW.

Geographical coverage: Worldwide

Sector: Burden of disease

Sub-sector: Epidemiology

Equity focus: None

Study population: Patients with myopia

Review type: Other review

Quantitative synthesis method: Systematic review

Qualitative synthesis method: Not applicable

Background: Myopia or nearsightedness is a refractive error caused by excessive axial elongation. Myopia can be corrected optically by glasses, contact lenses or refractive surgery. Nevertheless, it has been associated with complications, such as myopic macular degeneration (MMD), retinal detachment (RD), cataract and open angle glaucoma (OAG). These complications can lead to irreversible visual impairment later in life. Although the association with myopic complications has been well established, precise risk estimates of MMD, RD, cataract and OAG per degree of myopia are yet unknown.

Objectives: To determine the risk between degree of myopia and myopic macular degeneration (MMD), retinal detachment (RD), cataract, open angle glaucoma (OAG) and blindness.

Main findings:

Overall, authors found that although high myopia carries the highest risk of complications and visual impairment, low and moderate myopia also have considerable risks.

Findings of this review found that low, moderate and high myopia were all associated with increased risks of MMD (OR, 13.57, 95% confidence interval [CI], 6.18-29.79; OR, 72.74, 95% CI, 33.18-159.48; OR, 845.08, 95% CI, 230.05-3104.34, respectively); RD (OR, 3.15, 95% CI, 1.92-5.17; OR, 8.74, 95% CI, 7.28-10.50; OR, 12.62, 95% CI, 6.65-23.94, respectively); posterior subcapsular cataract (OR, 1.56, 95% CI, 1.32-1.84; OR, 2.55, 95% CI, 1.98-3.28; OR, 4.55, 95% CI, 2.66-7.75, respectively); nuclear cataract (OR, 1.79, 95% CI, 1.08-2.97; OR, 2.39, 95% CI, 1.03-5.55; OR, 2.87, 95% CI, 1.43-5.73, respectively); and OAG (OR, 1.59, 95% CI, 1.33-1.91; OR, 2.92, 95% CI, 1.89-4.52 for low and moderate/high myopia, respectively). The risk of visual impairment was strongly related to longer axial length, higher myopia degree and age older than 60 years (OR, 1.71, 95% CI, 1.07-2.74; OR, 5.54, 95% CI, 3.12-9.85; and OR, 87.63, 95% CI, 34.50-222.58 for low, moderate and high myopia in participants aged >60 years, respectively).

Although high myopia carries the highest risk of complications and visual impairment, low and moderate myopia also have considerable risks. These estimates should alert policy makers and health care professionals to make myopia a priority for prevention and treatment.

Regarding clinical management, the results suggest that vision-threatening complications can appear from moderate myopia onward. There is a strong relationship between myopia degree, age of the participant and visual impairment; more severe myopia results in an earlier onset of visual-threatening complications. Therefore, both factors should be taken into account regarding screening programmes and clinical guidelines.

Methodology:

Studies were included when the following criteria were met: (1) full text available; (2) written in English; and (3) subject of article was myopia complications, visual consequences of myopia, epidemiology of myopia, or epidemiology of visual impairment. All observational studies were considered for inclusion in the meta-analyses.

Authors conducted an extensive literature search in PubMed on myopia and myopia-related complications. Titles and abstracts of articles, published before 1 June 2019 were independently reviewed for relevancy by two authors. A manual search was additionally performed by screening of the references of the included articles.

The quality of studies was assessed using the criteria proposed by Sanderson et al. Crude odds ratios (ORs) were calculated for MMD when they were not reported in the studies. If the number of cases was zero, it was set to 1 for the OR calculation. Refractive error was categorised into five groups: no myopia (SER > -0.5 dioptre D]), any myopia (SER ≤ -0.5 D), low myopia (SER < -0.5 to > -3.00 D), moderate myopia (SER ≤ -3.00 to > -6.00 D), and high myopia (SER ≤ -6.00 D), in line with the most recent classification system.

Meta-analyses were performed using a previously validated method in Microsoft Excel 2010; forest plots for all complications and myopia categories were constructed in GraphPad Prism. A fixed- or random-effects model was used depending on the number of included studies and the critical value of the calculated Q statistic on the χ2 distribution. The Q statistic was calculated as the weighted sum of squared differences between individual study effects and the pooled effect across different studies. I² was calculated to investigate heterogeneity between studies, using the formula: ((Q-df)/Q)*100% (df represents degrees of freedom). A fixed-effects model was used if heterogeneity was low, that is, the calculated Q was lower than the critical value on a χ2 distribution, and a random-effects model was used otherwise.

Applicability/external validity: The authors conducted the first systematic review on this topic but faced several limitations. Different definitions were used for myopic complications, particularly for MMD and OAG. They tried to use guidelines from the International Myopia Institute for consistency, but sometimes had to rely on clinical judgement. Most studies only used colour fundus photographs, limiting the detection of all retinal complications. Thus, they focused on MMD, RD, cataract, and OAG. Despite axial length being more closely related to myopic complications than refractive error, they couldn’t study this for most complications due to missing eye biometry data.

Geographic focus: Included studies were conducted in a range of countries, including Australia, China, Taiwan, India, Japan, the United States, Singapore, the United Kingdom, Croatia, Sweden, Italy and Barbados.

Summary of quality assessment:

While two authors completed all key tasks relating to the selection, inclusion and synthesis of studies, the search was somewhat limited in that it only utilised one electronic database and no attempts were made to include unpublished material or to contact relevant experts. In addition, while it is stated that an assessment of the quality of individual studies was made, no information was included on the results of this assessment. While the approaches to the analysis of the data were generally robust, no analysis was undertaken by the risk of bias associated with the included studies, to ascertain how this may have affected the reported results. For these reasons, we attributed low confidence in the findings of this review.