Cataract remains the most common causes of blindness worldwide, followed by uncorrected refractive error, glaucoma, age-related macular degeneration (AMD), cornea-related diseases, trachoma and diabetic retinopathy, researchers believe.
The top causes have held their positions at least since 1990, but they contrast to high-income and Eastern European countries, where AMD is the second most common cause and glaucoma is the third, wrote Professor Rupert Bourne from Anglia Ruskin University and colleagues in the British Journal of Ophthalmology.
Meanwhile, uncorrected refractive error is the leading cause of moderate and severe vision impairment, followed by cataract, both worldwide and in the wealthy and Eastern European nations.
In a 2010 meta-analysis, Professor Bourne and colleagues found that 32.4 million people were blind worldwide in 2010, defined as a visual acuity less than 3/60 in the better eye, and 191 million had a moderate-to-severe vision impairment, defined as visual acuity not more than 6/18 but at least 3/60, a previous meta-analysis found. This made vision loss one of the greatest causes of disability.
To update this research, and add data on presbyopia, the team reviewed 46 cross-sectional population-based studies with visual acuity ascertained through clinical examinations, and combined the data in a new meta-analysis for 2015.
They used the United Nations Population Division’s forecasts to estimate prevalence for the causes of vision impairment up to 2020.
They found that the prevalence of blindness was 0.46% for men and 0.49% for women worldwide. The prevalence of moderate to severe vision loss was 2.79% for men and 2.99% for women. For mild vision loss (defined as visual acuity in the better eye worse than 6/12 to 6/18 inclusive), the prevalence was 2.49% for men and 2.6% for women.
Combining sexes, they found that the prevalence of blindness was 0.32% in wealthy and Eastern European nations in 2015, with 2.42% for moderate-to-severe vision impairment and 2.44% for mild vision impairment. The prevalence of presbyopia was 18.94% in these countries. Women were 12% more likely to be blind than men in these countries.
After adjusting for age, the researchers found that in the wealthy and Eastern European countries, the prevalence of blindness decreased from 0.26% in 1990 to 0.15% in 2015, while the prevalence of moderate to severe visual impairment decreased from 1.74% to 1.27%.
The researchers estimated that in 2015 there were 36.2 million blind people in the world, with 70,000 in Australasia, 980,000 in North America and 1.16 million in Western Europe.
Cataract caused 35.73% of the blindness in the world, making it the most common cause. It was followed by uncorrected refractive error, at 20.23%, glaucoma at 8.49% and AMD at 5.93%. In Western Europe, cataract was also the leading cause, at 21.42%. But it was succeeded by AMD at 15.39, then glaucoma at 13.5%, and then uncorrected refractive error at 13.6%.
In North America and Eastern Europe, the order of causes was similar, but AMD was even more important in Eastern Europe, causing 19.53% of blindness.
The order of the causes of blindness has remained constant since 1990, but both in the world, and in the rich and Eastern European countries, AMD has been declining in importance, the researchers found. In 1990, AMD caused 7.93% of the blindness in the world and 19.16% in Western Europe. They ascribed this trend to improved treatments for the neovascular form of the disease.
By contrast, diabetic retinopathy is becoming a more important cause of blindness. It accounted for 0.85% of the blindness in the world in 1990, but 1.6% in 2015. In Western Europe, it went from 2.42% to 3.3%.
This “likely reflects the increasing prevalence of diabetes mellitus in the general population and the ageing of the population, so that individuals with diabetes live to an age at which ocular complications of their systemic disease are experienced,” the researchers wrote.
The researchers found that 6.72% of people age 50 years or older in high-income or Eastern European countries were blind or vision-impaired. The most common cause of vision impairment in this group was uncorrected refractive error, with a prevalence of 3.3%. It was followed by cataract, with 1.7%, AMD with 0.81%, glaucoma with 0.33% and diabetic retinopathy with 0.28%.