Definitions and glossary (BVI)

Vision Impairment is the consequence of a functional loss of vision as a result of a disorder, disease or injury to the eye, optic nerve or brain.

A child or young person is thought to have a vision impairment if they have an eye condition that cannot be fully corrected using glasses.

The term vision impairment is used to cover a range of conditions and a range of levels of vision.  The term includes all blind and partially sighted people (OnlineInset.net).
 

1. Definition of Visual Acuity from the National Sensory Impairment Partnership (NatSIP) - 2015

Distance vision is measured and expressed as a fraction denoting the size of print on a Snellen chart seen at a distance, for example:

• 6/6: the child sees at 6 metres that which a fully sighted person would see at that distance (normal vision)
• 6/12: the child see at 6 metres that which a fully sighted person would see at 12 metres (vision required for driving) 
  6/18: the child sees at 6 metres that which a fully sighted person would see at 18 metres (impaired vision)
• The terms such as mild, moderate, severe and profound are used by NatSIP to describe distance vision loss, these are defined as: 
  • Mild Vision Loss - Within the range 6/12 to 6/18 Snellen/Kay (LogMAR 0.3-0.48)
  • Moderate Vision Loss - Less than 6/18 to 6/36 Snellen/Kay (LogMAR 0/5-0.78)
  • Severe Vision Loss - Less than 6/36 to 6/120 Snellen/Kay (LogMAR 0.8-1.3)
  • Profound Vision Loss - Less than 6/120 Snellen/Kay (LogMAR 1.32+) 

2. Functional Vision

• Can see to walk around
• Can recognise faces
• Can see print
• Believed to have residual vision where formal testing is not possible
• Defined as having sufficient vision for one of the following:
  • independent mobility
  • making social contacts
  • near vision 

3. Visual Field

• Everything that can be seen by an eye in any one position
• Includes central vision
• Includes peripheral vision

Useful links

A glossary of eye conditions can be found at: www.rnib.org.uk

Key documents