Low vision

What is low vision?

Specialist teacher Manju helps Sam Raj, who has low vision, at school © Fabienne Fossez / Sightsavers

Low vision is when, even after medical treatment, people have difficulty distinguishing objects and/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:

• 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
• 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
• 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.

Refractive error

A child has his eyes examined at school, Pakistan. © Jamshyd Masud / Sightsavers

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:

• screening: we identify individuals with poor vision which can be improved by spectacles or other optical devices. Last year we screened over 2 million people for refractive error.
• refraction: we evaluate the patient to determine what spectacles or device may be required.
• manufacture: we manufacture spectacles or an appropriate device and provide to those in need.

Common refractive errors:

• short sight (myopia)
• long sight (hypermetropia)
• Aging of the lens (presbyopia)
• Irregular curvature of the lens (astigmatism)
  

Low vision

Some people are still severely visually impaired even after correction, but their visual function can be greatly improved with the use of visual and non-visual aids.

Low vision aids

Visual aids

Visual aids for improving low vision work for those with visual capability of more than 1/60 (ie people who can see at a range of one foot what people with 'normal' vision would see at a range of 60 feet).

There are several types of low-vision device. Each works on particular form of low vision. Prescription is just the first step - it is also essential to motivate and train people to use the devices properly.

Visual aids include those that:

• help people seeing things close up. These are particularly useful for reading and to help children whose education would otherwise suffer. These include hand-held magnifying glasses and specially made, powerful spectacles.
• help people see things in the distance. These include telescopes.
• Technical enhancements such as closed circuit television, computer scanners and high tech image magnifiers.

Magnifiers

Some magnifiers can be made relatively easily and cheaply in optical workshops. Sometimes people in poorer countries use 'modified' plastic drainpipes fitted with a lens which acts as an effective reading aid.

Some studies show that over a third of children with low vision who cannot read would be able to with a simple magnifier.

Non-visual aids

Non-visual aids are often modifications to homes and everyday tools and equipment that make them low-vision friendly. These modifications are often quite cheap and easy to make.

Non-visual aids include:

• tilted desks for children, meaning they don't have to bend over flat desks to read text close-up.
• contrasting colours. A meal of rice and boiled fish can be difficult to distinguish for a low-vision person if served on a white plate. Certain colours and backgrounds can be combined to make text easier to read.
• size. Providing large felt tip pens or charcoal for children to write with, or using a photocopier to enlarge printed materials.
• lighting. Low-vision people needing more light can sit closer to windows or have better-positioned artificial light. People needing less light can benefit from dark glasses or large-brimmed hats.
• lines. A good way to aid mobility is through well-defined, contrasting-coloured lines to mark the edge of paths or steps.