Guidelines

Visual Impairment

Statistics

UK [1]

Other sources of UK statistics:

USA

Global [2]

Other sources of Global statistics:

What is it?

Individuals are registered blind if they have :

Individuals are registered as partially sighted if they have :

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
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
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
Sometimes 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].

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