What is most common disease that causes blindness?

Question: What is most common disease that causes blindness?
- Keywords:
  blindness,
  common,
  disease,
  human,
  illness
Asked by nnnie97 to Prateek on 22 Jun 2011.
- Prateek Buch answered on 22 Jun 2011:
  
  In richer countries it’s age-related macular degeneration (AMD), there are millions of people over the age of about 65 who suffer from this. In poorer countries the leading cause of blindness is still infection with things like bacteria – something that can be dealt with if people are provided with clean water. Cataracts that aren’t treated in time also cause blindness in some parts of the world

Question: What is most common disease that causes blindness?