Vision impairment types

Authored by Sarah Bell

This project will be exploring how both partial and full blindness can influence a person's relationship with the natural environment, and there are subtle distinctions that exist between different sight conditions - many of which may be important for how people interact with different spaces on a daily basis.

According to the Royal National Institute for the Blind, nearly two million people live with significant sight loss in the UK, but few are totally ‘black’ blind. Most people therefore have some degree of residual vision.

Vision impairments can affect both clarity of vision and visual field - how much of an environment the eyes can take in without moving. 

A range of online resources – such as the ‘Eye and Vision’ tool – have been developed to give an indication of how a person's vision can change with different eye conditions. Importantly, however, what people see is unique to them and may shift over time.  

Main eye conditions

  • Age-related macular degeneration - affects the central part of the field of vision (the ‘macula’, a part of the eye that focuses incoming rays of light to allow people to see detail and colour). 
  • Glaucoma – affects the optic nerve, which carries visual information from the eye to the brain. The central field of vision is generally last to be affected, often resulting in tunnel vision.  
  • Diabetic retinopathy – a complication of diabetes. High blood sugar levels can weaken the blood vessels in the back of the eye, constraining their oxygen supply and ultimately causing irreversible damage to the retina. 
  • Retinitis pigmentosa - a group of hereditary eye conditions that hinder the ability of varied parts of the retina to respond to light properly. 
  • Cataracts - a relatively common and mostly treatable eye condition, resulting in blurred, dimmed or even double vision as the lens of the eye becomes clouded, thereby compromising the flow of light to the back of the eye. 
  • Homonymous Hemianopia - experiences of stroke or traumatic brain injury can cause complete loss of one side of the visual field. 

It's also important to remember that not all sight loss is caused by physical damage to the eye itself. Cortical vision impairment can occur following damage to the visual centres of the brain i.e. the eyes may function normally but the visual centres of the brain are unable to interpret or make sense of what is being seen.

A wealth of information about eye conditions is available online; for more details try this from the RNIB.