Many countries around the world are seeing an increase in the average age of the population, as well as a shift in disease burden towards noncontagious diseases and disabilities, as a result of rising sociodemographic status and life expectancy. Most of the major causes of vision loss or blindness, such as cataracts and under corrected refractive error, are affected by this epidemiological shift, and they come at a high cost to both individuals and society. Cataract surgery and spectacle dispensing are two of the most cost-effective healthcare solutions accessible today. Scaling up existing healthcare systems to enable access to cataract surgery and spectacles is a key chance to address these reversible disorders.
The prevalence of different types of distance vision impairment was calculated using 512 data sources. At least one of the following causes was reported by 376 data sources: under corrected refractive error, cataract, glaucoma, age-related macular degeneration, myopic macular degeneration, or diabetic retinopathy. Blindness and MSVI caused by myopic macular degeneration had few data sources worldwide, with the majority of sources coming from China. As a result, researchers only reported myopic macular degeneration estimates for China. Data for children and young adults, as well as data for high-income locations, were both scarce globally. Researchers concentrated the analyses on adults aged 50 and older due to the scarcity of data at younger ages.
Researchers found that both cataract and under corrected refractive error are among the top three causes of blindness and MSVI in 2020. They estimated that over 15 million adults aged 50 and older are blind due to cataracts, and more than 86 million have MSVI due to refractive error that is under corrected. In 2020, cataract and under corrected refractive error account for half of all global blindness, and cataract and under corrected refractive error account for 75% of all global MSVI. Total blindness due to cataract and under corrected refractive error is a global problem with significant regional variation, but it has yet to be fully addressed in any region of the world, including high-income regions. Glaucoma, age-related macular degeneration, and diabetic retinopathy are the other major causes, accounting for more than 6 million blind adults aged 50 and older and more than 13 million adults aged 50 and older with MSVI in 2020. With the exception of diabetic retinopathy, all of the causes of blindness we discuss here have declined in age-standardised prevalence between 1990 and 2020. Given that the vast majority of vision impairment and blindness caused by cataract, under corrected refractive error, diabetic retinopathy, and glaucoma can be avoided with early detection and timely intervention, there is still a significant potential for reducing morbidity associated with these conditions.
Because cataracts and refractive error can be efficiently cured with surgery and spectacles, the World Health Organization (WHA) classified them as preventable causes of vision impairment. From 2010 to 2019, the WHA GAP established a goal of a 25% reduction in the crude prevalence of avoidable vision impairment. It emphasized the importance of lowering the prevalence of avoidable visual impairment among individuals aged 50 and older, as this is when the majority of vision impairment develops.
In all world regions in 2020, cataract remained the first or second leading cause of blindness and MSVI. Cataracts can only be treated operatively, by a trained surgeon working within a system capable of performing surgeries and managing any postoperative complications. Efforts to alleviate the problem have included mass campaigns, particularly in rural areas, as well as expanding surgical service capacity and accessibility. Because the prevalence of vision loss rises with age and is higher in women than in men, it remains a key target for vision loss prevention and gender equity. Women and the elderly, for example, have been shown to benefit from outreach screening. As a result, researchers advocate for the establishment of strong eye-care systems that are complemented by community outreach.
Under corrected refractive error is a common cause of vision loss that can be easily corrected with glasses, contact lenses, or refractive surgery. The most common causes of distance vision impairment are myopia, hyperopia, and astigmatism. Although cataract and under corrected refractive error were the leading causes of blindness and MSVI in 2020, glaucoma, age-related macular degeneration, and diabetic retinopathy also affected nearly 20 million people aged 50 and up. These illnesses are difficult to treat.
Glaucoma is the second most common cause of irreversible blindness and the fourth most common cause of MSVI, making it the most common cause of irreversible blindness and the second most common cause of irreversible MSVI. Glaucoma in eyes with dense cataracts may go undetected, resulting in undercounting of glaucoma-related irreversible blindness. Tonometry has not proven to be a useful screening technique for glaucoma-related vision impairment, and visual acuity assessment is not useful because vision impairment is a late symptom of glaucomatous optic neuropathy. In the majority of cases, glaucoma therapy can stop or slow the progression of the disease once it is detected, highlighting the importance of improving surveillance systems, highlighting risk among family members of cases, and the effectiveness of care once treatment is initiated.
Despite the fact that diabetic retinopathy was the least common cause of blindness in 2020 when compared to under corrected refractive error, cataract, age-related macular degeneration, and glaucoma, it was the only cause of blindness to show an increase in global age-standardised prevalence between 1990 and 2020. With more than 600 million people expected to have diabetes by 2040, and because people with diabetes are living longer, the number of people with diabetic retinopathy and vision impairment is expected to skyrocket.
Findings from this article show that diabetic retinopathy is still a recognized cause of vision loss. This is especially concerning among the younger, more economically active age groups. Research also found regional differences in the rate of diabetic retinopathy-related blindness, with increases in many parts of Asia and Sub-Saharan Africa, as well as high-income North America. The management of severe diabetic retinopathy, in comparison to cataract and under corrected refractive error, requires a disproportionate amount of resources, including the availability of ophthalmologists trained in laser and surgery.
Source: Pawar, S. (2021). Causes of blindness and vision impairment in 2020 and trends over 30 years, and prevalence of avoidable blindness in relation to VISION 2020: the Right to Sight: an analysis for the Global Burden of Disease Study. SSRN Electronic Journal. https://doi.org/10.2139/ssrn.3939242