Causes of blindness
When you think about it, the very act of seeing the world around us is an astonishing thing. It relies on the interaction between the brain and the eyeball, two extraordinarily complex organs, so it's hardly surprising that there are so many ways in which we can suffer sight loss or reduction.
Cataract
Cataract is the world's leading cause of blindness, with around 18 million people blind as a result. It is a clouding of the eye's lens - the part of the eye responsible for focusing light and producing clear, sharp images.
River blindess
River blindness is caused by a worm that breeds near fast-flowing rivers. It is a major cause of blindness in west and central Africa. Sightsavers is working to eliminate river blindness with the drug Mectizan®, which is donated by pharmaceutical company Merck & Co.
Trachoma
Trachoma is one of the most common causes of blindness in the developing world. It is linked to extreme poverty and poor sanitation.
Childhood blindness
Of the 45 million people worldwide who are blind, around 1.4 million are children under 16. The vast majority of childhood blindness happens before the age of five - a period when 75% of learning is through sight.
Diabetic retinopathy
Diabetic retinopathy is the sixth most common cause of blindness, affecting 1.8 million people globally. It is caused by damage to the small blood vessels in the retina at the back of the eye.
Glaucoma
Glaucoma is the third biggest cause of blindness worldwide. It affects around 60 million people, of whom about 4.5 million have become blind.
Low vision
Low vision is when, even after medical treatment, people have difficulty distinguishing objects and/or distances. People with low vision can be helped by changes made to their environment, such as painting the edges of stairs white so they can be seen more easily.