Visual Impairment

Statistics


UK [1]

  • About 2,000,000 people in the UK have significant sight loss
  • The vast majority of people with sight problems are older people, aged 65 and over
  • There are an estimated 25,000 children with sight problems in the UK, about 12,000 of these children also have other disabilities
  • At the end of March 2006 there were 364,615 people in the UK who were registered as severely sight impaired (blind) or sight impaired (partially sighted). A larger group of people also have significant sight loss, who do not fall into these narrow categories
  • Every day another 100 people start to lose their sight. This figure is based on the average number of people each day who registered as severely sight impaired or sight impaired
  • Over 50 per cent of all sight problems in older people are estimated to be due to untreated refractive error or cataracts
  • Seventy percent of blind and partially sighted adults have other disabilities or long term health problems in addition to their sight loss

Other sources of UK statistics:


USA


Global [2]

  • Globally, in 2002 more than 161 million people were visually impaired, of whom 124 million people had low vision and 37 million were blind. However, refractive error as a cause of visual impairment was not included, which implies that the actual global magnitude of visual impairment is greater
  • Worldwide for each blind person, an average of 3.4 people have low vision, with country and regional variation ranging from 2.4 to 5.5
  • Visual impairment is unequally distributed across age groups. More than 82% of all people who are blind are 50 years of age and older, although they represent only 19% of the world's population. Due to the expected number of years lived in blindness (blind years), childhood blindness remains a significant problem, with an estimated 1.4 million blind children below age 15
  • Available studies consistently indicate that in every region of the world, and at all ages, females have a significantly higher risk of being visually impaired than males
  • Visual impairment is not distributed uniformly throughout the world. More than 90% of the world's visually impaired live in developing countries

Other sources of Global statistics:


What is it?

Individuals are registered blind if they have :

  • a visual acuity of less than 3/60 Snellen or
  • a visual acuity of between 3/60 and 6/60 Snellen and a considerable contraction of their field of vision or
  • a visual acuity greater than 6/60 Snellen and a field contraction covering majority of the field

Individuals are registered as partially sighted if they have :

  • visual acuity of between 3/60 and 6/60 Snellen and a full field of vision or
  • a visual acuity of between 6/60 and 6/24 Snellen and a moderate contraction of their field of vision or
  • a visual acuity up to 6/18 Snellen, or even better, with a gross field defect


Types

Here is a list of eye conditions:

Aniridia
Aniridia is a rare congenital eye condition causing incomplete formation of the iris. This can cause loss of vision, usually affecting both eyes. In Aniridia, although not entirely absent, all that remains of the iris, the coloured part of the eye, is a thick collar of tissue around its outer edge. The muscles that open and close the pupil are entirely missing. The appearance of a "black iris" is the result of the really enormous pupil.

Cataracts
Picture showing the effect cataracts have on a persons vision A cataract is a clouding of part of your eye called the lens. Your vision becomes blurred because the cataract is like frosted glass, interfering with your sight. It is not a layer of skin that grows over your eye.

 

 

 

Colour blindness
Colour blindness is the reduced ability to distinguish between certain colours or wavelengths of light. To see colours properly, light detecting photoreceptor cells, called cones, are needed in the retina of the eye. Three different types exist, each containing a different photopigment: the short-wave (S, sometimes called 'blue'), middle-wave (M, sometimes called 'green')- and long-wave (L, sometimes called 'red') sensitive cones. These have distinct, spectral sensitivities, which define the probability curve of photon capture as a function of wavelength. The absorbance spectra of the S-, M- and L-cone photopigments overlap considerably, but have their wavelengths of maximum absorbance in different parts of the visible spectrum. If one or more of these types of cells is faulty then colour blindness results.

Diabetic retinopathy
Picture showing the effect diabetic retinopathy has on a persons vision Diabetes can affect the eye in a number of ways. The most serious eye condition associated with diabetes involves the retina, which is the light-sensitive tissue lining the back of the eye and, more specifically, the network of blood vessels lying within it.

 

 

Glaucoma
Glaucoma is the name for a group of eye conditions in which the optic nerve is damaged at the point where it leaves the eye. This nerve carries information from the light sensitive layer in your eye, the retina, to the brain where it is perceived as a picture. Your eye needs a certain amount of pressure to keep the eyeball in shape so that it can work properly. In some people, the damage is caused by raised eye pressure. Others may have an eye pressure within normal limits but damage occurs because there is a weakness in the optic nerve. In most cases both factors are involved but to a varying extent. Eye pressure is largely independent of blood pressure.

Macular degeneration
Picture showing the effect macular degeneration has on a persons visionSometimes the delicate cells of the macula, which is responsible for what we see straight in front of us, allowing us to see fine detail for activities such as reading and writing, as well as our ability to see colour, become damaged and stop working, and there are many different conditions which can cause this. If it occurs later in life, it is called “age-related macular degeneration”, also often known as AMD.

 

Nystagmus
Nystagmus is characterised by an involuntary movement or shake in one or both eyes. There are a variety of different categories of the condition, the nomenclature of which is usually based on the direction or type of movement. There are a number of different causes of nystagmus and it can be congenital (present at birth) or acquired (as a result of, for example, disease or injury). The degree of vision impairment experienced by different people with nystagmus varies from a slight blurring of vision to being registered blind. With the exception of people with other eye conditions, the majority of people with nystagmus are partially sighted and not completely blind.

Retinitis pigmentosa
Retinitis pigmentosa (RP) is the name given to a group of hereditary eye disorders. These disorders affect the retina, which is the light-sensitive tissue lining the back of the eye, in which the first stages of seeing take place. In RP, sight loss is gradual but progressive. It is unusual for people with RP to become totally blind as most retain some useful vision well into old age.

There are several other eye conditions.


Further information


[1] RNIB (2008) Statistics - numbers of people with sight problems in the UK. [accessed 25/02/08].
[2] World Health Organisation (2004) Magnitude and causes of visual impairment. [accessed 29/01/08].