Blindness

Blindness is the inability to see. The leading causes of chronic blindness include cataract, glaucoma, age-related macular degeneration, corneal opacities, diabetic retinopathy, trachoma, and eye conditions in children (e.g. caused by vitamin A deficiency). Age-related blindness is increasing throughout the world, as is blindness due to uncontrolled diabetes. On the other hand, blindness caused by infection is decreasing, as a result of public health action. Three-quarters of all blindness can be prevented or treated.

Definitions

There are 4 levels of visual function, according to the International Classification of
Diseases -10 (Update and Revision 2006): 

• normal vision
• moderate visual impairment
• severe visual impairment
• blindness.

Moderate visual impairment combined with severe visual impairment are grouped under the term “low vision”: low vision taken together with blindness represents all visual impairment.

The causes of visual impairment

Globally the major causes of visual impairment are:

• uncorrected refractive errors (myopia, hyperopia or astigmatism), 43 %
• unoperated cataract, 33%
• glaucoma, 2%. 

Who is at risk? 

Approximately 90% of visually impaired people live in developing countries. 

People aged 50 and over 

About 65 % of all people who are visually impaired are aged 50 and older, while this age group comprises about 20 % of the world's population. With an increasing elderly population in many countries, more people will be at risk of visual impairment due to chronic eye diseases and ageing processes.

Children below age 15

An estimated 19 million children are visually impaired. Of these, 12 million children are visually impaired due to refractive errors, a condition that could be easily diagnosed and corrected. 1.4 million are irreversibly blind for the rest of their lives and need visual rehabilitation interventions for a full psychological and personal development.

source: who.int