The eye The eyes are undoubtedly the most sensitive and delicate organs we possess, and perhaps the most amazing. They present us with the window through which we view the world, and are responsible for four fifths of all the information our brain receives which is probably why we rely on our eyesight more than any other sense.
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The images we see are made up of light reflected from the objects we look at. This light enters
the eye through the cornea. Because this part of the eye is curved, it bends the light, creating
an upside-down image on the retina (this is eventually put the right way up by the brain).
Focusing on a nearby object Focusing on a distant object
What happens when light reaches the retina?
The retina is a complex part of the eye, but only the very back of it is light-sensitive. This part of the retina has roughly the area of a 10p coin, and is packed with photosensitive cells called rods
and cones. These allow us to see images in colour and detail, and to see at night.
Cones are the cells responsible for daylight vision. There are three kinds - each responding to a
different wavelength of light: red, green and blue. The cones allow us to see in colour and
detail.
Rods are responsible for night vision. They are sensitive to light but not to colour. In darkness,
the cones do not function at all.
Focusing the image
The lens focuses the image. It can do this because it is adjustable - using muscles to change
shape and help us focus on objects at different distances. The automatic focusing of the lens is
a reflex response and is not controlled by the brain.
Sending the image to the brain
Once the image is clearly focused on the sensitive part of the retina, energy in the light that
makes up that image creates an electrical signal. Nerve impulses can then carry information
about that image to the brain through the optic nerve.
y daylight - some controversially believe ultraviolet light worsens cataract. This is
unproven and impossible to combat if true.
Cataracts and poverty
Removing cataract (the clouding of the eye's lens) is a relatively simple surgical procedure. It iscommon and easily accessible in developed countries. But in the countries where Sightsavers
works, many people with cataracts are yet to benefit.
Why is this?
y lack of awareness in some areas about the number of people with cataracts, and how
best to diagnose them
y lack of staff and equipment to significantly reduce the growing backlog of cataract
operations needed.
There are also reasons why prospective patients may be wary of an operation:
y they may not know that the operation is simple and safe
y they may have heard of someone who had a bad experience while having an operation
y they may live far from towns, and getting to hospital may involve a lot of travel and
expense. This is never easy for a blind person.
y as well as the travel costs, people will not be able to work immediately after the
operation and will lose income
y people sometimes expect to go blind as a natural part of ageing and are unaware of how
simple it is to have their sight restored
Sightsavers is raising awareness of the need for cataract treatment and providing it wherever
possible.
Our work with cataract
Our cataract work involves a number of different aspects:
Screening and ref erring those in need
We train local community health workers to identify those in need of cataract treatment,
ensuring that they are referred to an ophthalmic specialist for an operation.
Providing f ree surgery and transport
The only way to treat cataract (the clouding of the eye's lens) is by surgery. This involves
removing the cloudy lens, leaving the capsule that contains it intact. A plastic lens is inserted,
meaning that there is no need to wear special glasses after the operation.
Trachoma is linked to extreme poverty and poor sanitation. It is triggered by bacteria that cause
repeated conjunctivitis, irritating the eyes and creating a mucous discharge. Although the
conjunctivitis clears up after a month or so, it is easily spread. This is particularly the case in
places where there is little water for people to wash their hands and faces regularly.
How trachoma causes corneal damage:
y reducing the amount of tears produced
y making it difficult to close the eyelids (which lubricate the eye and help flush away dust
and dirt)
y triggering trichiasis, where the eyelid and eyelashes turn in on the eye.
How does it spread?
y The discharge from infected eyes attracts flies that then land on other people's skin.
People in crowded households or neighbourhoods are particularly vulnerable.
Trichiasis
y Each infection of trachoma leads to a small amount of scarring on the cornea and
conjunctiva. This scarring builds up over years of repeated infection until trichiasis sets
in.
Trichiasis is when this scarring causes the eyelid to turn inwards, making eyelashes scratch the
eyeball. Each time the eyelashes are lowered to blink, the cornea - which enables the eye tofocus - is put at risk. Eventually it becomes opaque, causing poor vision and eventual
irreversible blindness.
People often try to pull out the eyelashes themselves, put powder on their eyelids, or use tight
headscarves to pull up the skin around the eye to restrict blinking. None of these provides a
long-term solution.
Tackling trachoma
Sightsavers is part of the Global Elimination of Trachoma by 2020 programme, working
alongside the World Health Organization and other voluntary organisations.
Since its launch in 1998 the programme has treated more than seven million people and
reduced active trachoma in children by 50 per cent.
Sightsavers follows the SAFE strategy for treating trachoma. (Surgery, Antibiotics, Facial
y promoting advocacy to ensure that governments of developing countries do not allow
blind children to be discriminated against, such as by being excluded from education.
Low vision
Low vision is when, even after medical treatment, people have difficulty distinguishing objectsand/or distances. People with low vision can be helped by changes made to their environment,
such as painting the edges of stairs white so they can be seen more easily, or specially made
devices.
Measuring low vision
Eye care specialists measure sight against a standard known as '20/20' vision. This based on
what most people are able to see on a standard eye-test chart at a distance of 20 feet (in
metres this is called 6/6 vision). If you can read the chart at 20 feet you have 20/20 or 'normal'
vision.
The range of low vision:
y in mild cases of low vision, someone looking at a standard eye chart from 6 feet away
will see what somebody with 'normal' or 20/20 vision sees from 18 feet away
y in extreme cases, low vision means that a person standing 3 feet from the eye chart will
see the equivalent of what a person with 'normal' vision will see 60 feet away
y if someone's sight is any worse than this, they are classified as blind.
Low vision is officially defined as 'anybody who has an optimum corrected vision of less than
6/18 to 3/60 in their better eye'.
'Optimum corrected vision' means the 6/18 to 3/60 vision is enabled the aid of standard
corrective visual devices - usually spectacles.
Many diagnosed with low vision can be helped by surgical treatment, and do not need low-
vision aids. Even people with less than 3/60 vision can be helped.
Ref ractive error
Refractive error is an eye disorder meaning the shape of the eye does not bend light correctly,
resulting in a blurred image. The disorder can be simply diagnosed, measured and corrected
with spectacles, yet approximately 8.2 million people remain functionally blind due to
uncorrected refractive error.
Sightsavers works in several ways to improve the vision of people with refractive error: