Epidemiology and disease burden of pathologic myopia and myopic choroidal neovascularization: an evidence-based systematic review

Methodological quality of the review: Low confidence

Author: Wong TY, Ferreira A, Hughes R, Carter G, Mitchell P.

Region: Netherlands, Denmark, Italy, United States of America (USA), China, Japan, Hong Kong, Canada, Israel, United Kingdom (UK), Germany, Pakistan, India and Australia.

Sector: Epidemiology, disease burden

Sub-sector: Pathologic myopia, myopic choroidal neovascularization, vision impact.

Equity focus: None specified

Review type: Effectiveness review

Quantitative synthesis method: Narrative analysis

Qualitative synthesis methods: Not applicable

Background

A proportion of people with myopia have pathologic myopia, which is characterized by excessive and progressive elongation of the globe, and is now considered to be an important cause of impaired vision and blindness worldwide. Choroidal neovascularization (CNV) is a frequent complication associated with pathologic myopia that threatens vision, and is characterized by the occurrence of newly formed abnormal blood vessels that grow under the retinal pigment epithelium or retina and can penetrate the Bruch membrane to extend into the subretinal space, with subsequent scarring. Data on the epidemiology of pathologic myopia and CNV secondary to pathologic myopia (myopic CNV) in the literature are inconsistent, and the impact of this condition on vision remains unclear.

Research objectives

To summarize the epidemiology of pathologic myopia and myopic choroidal neovascularization (CNV) and their impact on vision.

Main findings

In total, of the 38 eligible studies, 24 were publications primarily focusing on the prevalence or incidence of pathologic myopia, and 13 of these included data on pathologic myopia as a cause of low vision or blindness. The remaining 14 studies focused on CNV, namely the prevalence and location of CNV, associated risk factors, and the changes in visual acuity during follow-up of untreated patients with myopic CNV. Studies were conducted in Netherlands, Denmark, Italy, USA, China, Japan, Hong Kong, Canada, Israel, UK, Germany, Pakistan, India and Australia.

Population-based studies reported pathologic myopia to be the first to third most frequent cause of blindness. The prevalence of pathologic myopia was reported to be 0.9%-3.1%, and the prevalence of visual impairment attributable to pathologic myopia ranged from 0.1%-0.5% (European studies) and from 0.2%-1.4% (Asian studies). The prevalence of CNV in individuals with pathologic myopia was reported to be 5.2%-11.3%, and was bilateral in approximately 15% of patients. All studies of visual outcome in patients with myopic CNV (duration ranging from less than three months to 21.5 years) reported deterioration in best-corrected visual acuity over time. Older age, subfoveal CNV location, and larger baseline lesion size were predictors of worse visual outcomes.

The authors concluded that a substantial proportion of patients with myopia develop myopic CNV, which mostly causes a significant progressive decrease in visual acuity. They also noted that this condition should therefore be a target for new treatment strategies.

Methodology

Studies were included if they were considered to concern pathologic myopia or if they concerned pathologic, degenerative, progressive, and malignant myopia.

Authors conducted a search of all English-language studies only in PubMed and Embase in 2011 with no time limits and which were updated in 2012. To supplement the primary search, the Cochrane Library and the University of York Centre for Reviews and Disseminations databases were searched. Reference lists of included studies were also reviewed.

Articles identified from the searches were screened by a single researcher and checked by a second researcher and data extraction was conducted by two researchers independently. Discrepancies were resolved through discussion with a third researcher. The authors did not report assessing the quality and risk of bias of included studies.

Authors conducted a narrative synthesis of included studies.

Applicability/external validity

The authors noted that this review identified substantial evidence indicating that pathologic myopia has a detrimental effect on vision and is an important cause of low vision and blindness. Population-based surveys reported pathologic myopia to be the most common causes of blindness or low vision, with pathologic myopia being the primary cause in approximately 7% of individuals with low vision or blindness in European populations and in 12-17% of individuals in Asian populations.

Geographic focus

The authors included data from all income settings including India and Pakistan (lower- and middle-income setting) and China (upper- and middle-income setting). They reported that studies from India (Hyderabad) reported pathologic myopia as a cause of low vision or blindness in individuals seen at a tertiary care eye hospital. Nevertheless, findings may not be applicable to other countries.

Quality assessment

Overall there is low confidence in the conclusions about the effects of this study as important limitations were identified. The authors conducted a narrative synthesis of the findings, which seemed appropriate due to the heterogeneity of the included studies. However, they did not report explicitly the selection criteria used and did not conduct a comprehensive search of the literature so that we can be confident that relevant studies were not omitted. Although the authors used appropriate methods in terms of study selection and data extraction, they did not report the critical characteristics, nor did they state the risk of bias of included studies. Therefore, it is not clear what impact these limitations of included studies had on the validity of this reviews’ findings.