The eye and Myopia
Light coming into the eye is focused onto the retina – an area on the rear wall of the eyeball. 70% of light entering the eye is focused by the cornea (a clear dome which forms the outer covering of the pupil). The rest is focused by the lens, which sits behind the cornea. If the light is focused properly on the retina, we see a clear image. If the light focuses in front of the retina, the image is fuzzy.
With myopia, the cornea is too curved or the eyeball too long. This means that images are focused in front of the retina rather than directly on it.
Who gets Myopia?
Myopia most commonly develops in childhood or early teens (between ages 8 and 14). There may also be a link between myopia and prolonged close-up work, such as reading or sitting close to the television, although there is little scientific evidence for this.
Temporary short-sightedness, called pseudomyopia, can be caused by a number of diseases or certain drugs. For example, myopia may be the first sign of type-2 (non insulin-dependent) diabetes. Symptoms of pseudomyopia usually clear up if the underlying cause is treated.
On occasions, the eyeball continues to grow and myopia becomes progressively worse. This is called pathological myopia. People with this type of myopia are at an increased risk of developing certain other eye problems, which can sometimes lead to blindness. For example, a few people with severe myopia may get retinal detachment, which is when the retinal lining separates from the back wall of the eye. This requires urgent surgical treatment to prevent permanent loss of vision.
Children younger than eight may not realise they have blurred vision. Parents or teachers may suspect a child has myopia if they squint or frown a lot, hold books close to their face, or have trouble seeing a blackboard, television or cinema screen.
Children under 16 should be tested once every year, if they have no problems. If a problem has been identified, they should have a sight test every six months. Adults should have a test every two years, or more frequently if there are problems.
Myopia is usually diagnosed by reading a standard chart (called a Snellen chart) from a distance of six metres. The chart has large letters at the top and small ones at the bottom. A person with normal eyesight will be able to read the chart at six metres. This is called 6/6 vision. If they have myopia, their vision may be 6/12. This means that at six metres they can read what a person with normal vision can read at 12 metres.
Contact lenses or spectacles?
Spectacles can be worn by people of all ages, however, they may get in the way of some types of work or sports, and they fog up in humid or cold weather. Some people find them uncomfortable or unattractive to wear. Contact lenses give better peripheral vision than spectacles, and come in a wide range to meet individual needs.