The main symptom of short-sightedness (myopia) is distant objects appearing blurred, while near objects can still be seen clearly.

When does short-sightedness occur?

Short-sightedness usually starts to develop around puberty, but it can develop at any age, including in very young children.

It's unusual for the condition to start after the age of 30, although older people may become short-sighted as a result of cataracts (cloudy patches that develop in the lens of the eye).

Younger children may think that blurred vision is normal, so their symptoms may only be noticed after they start school and have difficulty reading the blackboard.

Short-sightedness often gradually gets worse as a child gets older. This is because as the child grows, their eyes grow longer. The condition tends to stabilise after a person is fully grown, although sometimes it can progress until the mid- to late-20s.

In older people, the onset of short-sightedness can be an early indication that a cataract is forming. Cataracts occur when the eye's lens, which is usually clear, starts to become opaque (cloudy), resulting in blurred or cloudy vision. They are usually associated with ageing.

If you or your child notice the signs of short-sightedness, you should make an appointment for a sight test with an optometrist (optician).

Read more about NHS opticians.

Severity of short-sightedness

Healthcare professionals use a measurement called dioptres (D) to describe how severely short-sighted a person is. The higher the measurement, the longer a person's eye or the more curved their cornea (the transparent layer at the front of the eye).

For short-sightedness, dioptres are written as a negative measurement (-3D), whereas in long-sightedness they are written as a positive measurement (+3D). 

There are three classifications used to describe the severity of short-sightedness. These are outlined below.

Mild myopia

Mild myopia is a measurement of -0.5D to -3D. This is the most common type of short-sightedness. You may be able to manage without wearing glasses or contact lenses, but they may be recommended for certain activities, such as driving or watching television.

Moderate myopia

Moderate myopia is a measurement of -3D to -6D. If you have moderate myopia, it is likely that you will have to wear glasses or lenses all the time.

High myopia

High myopia is a measurement of more than -6D. If you have high myopia, you will only be able to see objects clearly without glasses if you hold them very close to your eye.