Diagnosing short-sightedness

You can find out if you have short-sightedness (myopia) by having an eye test at your local opticians.

Find an opticians near you .

You should have a routineeye test at least every two years, but you can book a test at any point if you have any concerns about your or your child's vision.

For some people such as childrenunder 16, orthose under 19 and in full-time education eye tests are available free of charge on the NHS. Read about NHS eyecare entitlements to check if you qualify.

What happens during an eye test

Your eyes will usually be tested byan optometrist (someone who's been specially trained to examine the eyes).

It can be difficult to examine young children's eyes, so they may sometimes need to be referred to a local hospital eye service for an eye test, and they may need eye drops to dilate the pupil of the eye to get accurate measurements.

A number of different testswill usually be carried out as part of your eye test, possibly including:

• measurements of the pressure inside your eyes
• checks to measure how well your eyes work together
• visual acuity tests where you're asked to read from a chart that has rows ofletters that getsmaller on each line
• retinoscopy where a bright light is shone into your eye to see how your eye reacts to it

If the tests detect a possible problem with your distance vision, you may be asked to repeat the visual acuity tests while different strength lenses are placed in front of your eyes. This will help the optometrist to determine what your glassesprescription should be.

Understanding your glasses prescription

If an eye test finds that you're short-sighted, you'll be given a prescription that describes what lenses you need to improve your vision. This can be used to make glasses or contact lenses.

Your prescription will usually consist of three main numbers for each eye. These are:

• Sph (sphere) a positive number here indicates that you're long-sighted, while a negative number indicates that you're short-sighted
• Cyl(cylinder) this number indicates whether you have astigmatism (where the front of your eye isn't perfectly curved)
• Axis this describes the angle of any astigmatism you have

If you're short-sighted, the Sph number is the most relevant. This is given in a measurement called dioptres (D), which describes how severely short-sighted you are.

A score of -0.5Dto -3D is usually considered to be mild myopia, while a scoreof more than -6D is considered to be severe or "high" myopia.