Globally, the leading causes of vision impairment are:

• uncorrected refractive errors
• cataract
• age-related macular degeneration
• glaucoma
• diabetic retinopathy
• corneal opacity
• trachoma

There is substantial variation in the causes between and within countries according to the availability of eye care services, their affordability, and the eye care literacy of the population. For example, the proportion of vision impairment attributable to cataract is higher in low- and middle-income countries than high-income countries. In high income countries, diseases such as glaucoma and age-related macular degeneration are more common.

Among children, the causes of vision impairment vary considerably across countries. For example, in low-income countries congenital cataract is a leading cause, whereas in middle-income countries it is more likely to be retinopathy of prematurity. As in adult populations, uncorrected refractive error remains a leading cause of vision impairment in all countries amongst children