Cataract or uncorrected refractive errors account for most vision loss among all ages worldwide.
An increase in blood glucose also called blood sugar, is termed as diabetes. Blood glucose is the primary source of energy and comes from the food we intake. There are two main types of diabetes – Type 1 and Type 2 diabetes. Type 1 diabetes is an autoimmune disease, and Type 2 diabetes is caused by insulin resistance and pancreatic failure. High glucose levels lead to abnormal blood flow in the eyes, which causes retinopathy—severe diabetic retinopathy results in vision impairment.
The leading causes of blindness worldwide in 1990 and 2010 were cataract (39% and 33%, respectively), uncorrected refractive error (20% and 21%), and macular degeneration (5% and 7%). For Moderate to Severe Visual Impairment (MSVI), the leading causes were uncorrected refractive error (51% and 53%), cataract (26% and 18%), and macular degeneration (2% and 3%) (Refer to Page No.1 of 'Causes of vision loss worldwide, 1990–2010: a systematic analysis'). The prevalence of blindness due to diabetic retinopathy is lower from 1990 to 2020. Among the global population, about 36 million were blind in 2015 because of cataract followed by uncorrected refractive error, glaucoma, age-related macular degeneration, corneal opacity, trachoma, and diabetic retinopathy. Blindness in those aged 50 years and older in 2015 was due to cataract followed by uncorrected refractive error and glaucoma (Refer to Page No.7 of 'Global causes of blindness and distance vision impairment 1990–2020: a systematic review and meta-analysis').
A recent global survey conducted in 2020 reveals that 671 million people were affected by uncorrected refractive error, and 100 million people have vision loss from cataract. Also, the predictions by The Lancet made are lower than the recent survey results (IAPB).