Short-sightedness

About short-sightedness
To understand what myopia is, it helps to know how our eyes focus. The diagrams below show normal vision, short-sightedness and corrected myopia.



Normal vision
When you look at something, light rays from the object pass into the eye through your cornea - the clear structure at the front of your eye - then through the lens towards the retina at the back of your eye. In a healthy eye the lens and cornea focus the light rays on a small area of your retina so that you can see the object clearly.

Short-sightedness or myopia
If your cornea is too curved, or your eyeball too long, light rays from distant objects focus in front of your retina. This makes objects seem fuzzy or blurred.

Nearby objects don't look fuzzy, because the light rays enter your eye at a slight angle. This means they focus on your retina properly.

Corrected myopia
The bottom diagram shows how a lens - from a pair of glasses or contact lenses - refocuses light rays onto your retina, returning your vision to normal.

Symptoms
Short-sightedness causes distant objects to appear blurry and unfocused, while nearby objects remain in focus.

Causes
Myopia usually develops in children or young teenagers. You are more likely to develop myopia if it runs in your family.

Temporary short-sightedness, called pseudomyopia, can be caused by certain diseases or drugs. For example, myopia can be the first sign of type 2 (non-insulin-dependent) diabetes. Pseudomyopia usually clears up if the underlying cause is treated.

Diagnosis
If you are straining to see things in the distance you should visit an optometrist and get your eyes tested. It's important to get regular eye tests. As well as diagnosing any vision problems they can reveal other serious illnesses, such as diabetes or high blood pressure.

According to the College of Optometrists, you should have an eye test every two years. Depending on your age, or if you have any known sight problems or illnesses that affect vision, you may need one more often. Ask your optometrist or GP for more advice.

Some people are only mildly short-sighted and need to wear glasses or contact lenses only occasionally, such as when driving. Others need to wear glasses or contact lenses all of the time.

Young children may not realise that they have blurred vision. If a child frowns or squints a lot, or has trouble seeing the TV, then he or she might have myopia.

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.

Treatment
Glasses and contact lenses
Short-sightedness can usually be corrected by wearing glasses or contact lenses. Some people wear contact lenses, but others feel more comfortable in glasses. Your optometrist will discuss with you what options are available.

Contact lenses tend to be more expensive than glasses, and you have to be comfortable touching your eyes to use them. They need to be kept clean and some types require a lot of care. A popular type of modern contact lens is the daily disposable contact lenses, which are worn for one day and then thrown away. When you wake up the next morning you put in a brand new pair. There is no cleaning or storing with these lenses.

Glasses are usually recommended for children. They are also easier than contact lenses for older people. Glasses are also a better option for those people who find contact lenses fiddly and don't like touching their eyes.