Although nowadays many of the diseases that used to cause blindness such as cataracts and glaucoma, have received effective treatments, many are the conditions which continue to affect the vision to such an extent that they can cause severe visual impairment.
So far no one has given an international definition for blindness. Every country uses its own definition according to its own laws. For Greece, legally blind are those who even with the use of corrective lenses have a visual acuity of less than 1/20. In other words, they are not able to distinguish from a distance of one metre, something that a person with normal vision can distinguish from twenty.
Partially sighted or amblyopic is considered one that even with the use of corrective lenses has a visual acuity between 1/20 and 1/10 of the normal range.
It is obvious that the definition of blindness includes not only people who "see darkness" but also people with light perception who can perceive the presence of large objects such as trees or cars.
When parents learn that their child suffers from severe visual impairment which cannot be cured, they really despair.
Vision is undoubtedly valuable, but certainly not the only way to know our environment.