What is blindness? > Blindness information

From the physiological point of view blindness can be defined as the state of sight deficiency. However, the definition, as it is applied to people who are legally classified as blind, is more complex. Total blindness is a permanent and complete loss of sight when the visually handicapped person cannot perceive the light. The significant decrease of vision functions is labeled as practical blindness.

The seriousness of sight handicap is defined by the vision sharpness expressed by Snellen ratio. For example strong shortsightedness is defined as the quality of vision expressed in Snellen ratio 1/10 or less. This means that practically blind individual has to stand 6 meters from the object to see it as clearly as the normally sighted person would see it from the distance of 60 meters.

The World Health Organization (WHO) defines legal blindness as the vision 20/400 (3/60) or less in stronger eye with correction or visual field smaller than 10 degrees.

Approximately 10 percent of people considered to be legally blind by any measurements are actually without the sight. Others have at least some degree of vision, from the perception of light to relatively good sharpness. Those, who are not legally blind but in spite of this they have a serious visual disruption, are considered to be short-sighted.