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Eyesight tests – what can they show me?

Many people think of eyesight tests as a way of checking whether they need glasses, or finding out if their contact lens prescription is still correct. However, eyesight tests can give the first warning of a number of different conditions that also affect your general health. As a thorough eyesight test, carried out by a qualified optometrist usually takes only about 20 to 30 minutes, this is a personal health check that you shouldn’t miss.

This article on eyesight tests is written by Kathryn Senior, a freelance journalist who writes health, medical, biological, and pharmaceutical articles for national and international journals, newsletters and web sites.

Eyesight tests for vision

Most eyesight tests are done to assess the type of vision you have and to detect any problems that need to be corrected by glasses or lenses.

Problems with the shape of the eyeball, the shape of the lens, the quality of the lens or the way that information is transmitted to the brain can all cause poor vision. Vision changes with age – we all succumb to age-related long-sightedness around the age of 45. It is important to have regular eyesight tests at this age to avoid eyestrain and headaches.

Standard eyesight tests can pick up the following vision problems:

Short sight, also known as near sight or myopia; you can see close objects clearly but it is difficult to make out distant objects very well – these tend to be blurred. Short sight happens when the lens focuses the image in front of the retina, and is because the eyeball is too long or the cornea is too steep.
Long sight, also known as far sight or hyperopia; you can see distant objects clearly but near objects are blurred. Long sight occurs when the lens focuses the image behind the retina, and is because the eyeball is too short.
Astigmatism; if you have astigmatism you may find it hard to focus on horizontal and vertical lines at the same time and your ability to judge distances and depth can be poor. Astigmatism arises when the curve in the cornea or lens is abnormal.
Presbyopia; this is long sight that develops through aging, because the lens gradually becomes less flexible, making it harder for the eye muscles to change the shape of the lens.

The results of eyesight tests are used by the optometrist to put together an accurate prescription for glasses or contact lenses to correct your vision as much as possible. Most people need to have repeat eyesight tests to check their vision every 2 years. Regular eyesight tests can also pick up more serious illnesses such as glaucoma and age-related macular degeneration (AMD) as well as diabetes and high blood pressure.

Eyesight tests for glaucoma

If you have glaucoma, high pressure inside the eye causes damage to the optic nerve, leading to loss of vision and blindness. Around 1 in 50 people in the UK over 40 have some form of glaucoma, and the risk of glaucoma increases as we get older. The most common form of glaucoma is open-angle or chronic glaucoma, which happens when the tubes that drain fluid from the eyes become partly blocked. Because the fluid cannot drain, the pressure in the eye increases, damaging the optic nerve and the nerves in the retina. If glaucoma is found early and treated, this can prevent damage to your vision.

In an eyesight test for glaucoma, the optician puffs air onto the surface of the eye to measure the intraocular pressure – the pressure inside the eye. Other eyesight tests for glaucoma include checking your peripheral vision as a problem with this is often the first sign of glaucoma. You will be asked to look at a main light and then watch for spots of light coming into your field of view over a few minutes, activating a counter whenever you see a spot of light appear. A computer plots your responses and can detect if you have any ‘blind areas’ in your peripheral vision.

Eyesight tests for macular degeneration

Eyesight tests such as the Amler test can diagnose age-related macular degeneration (AMD). AMD occurs when the macula, an area on the retina that helps with accurate vision, becomes damaged or distorted by an overgrowth of blood vessels. As AMD progresses, central vision is lost, making it hard to read or to recognise faces. The Amsler test involves looking at a grid of squares with a dot in the middle – if the grid seems distorted when you stare at the central dot this may indicate AMD.

Eyesight tests for other conditions

During the eyesight test, the optometrist will examine your retina using a slit lamp. This can detect the first signs of undiagnosed diabetes, and monitor the progression of diabetic retinopathy, a common cause of blindness in people with diabetes. Changes in the retina that are also visible during eyesight tests may also indicate the early signs of high blood pressure. The optometrist also uses the slit lamp to look for cataracts and corneal ulcers. Optometrists can diagnose and treat a number of eye conditions including infective conjunctivitis, allergic conjunctivitis, superficial eye injuries, blepharitis and dry eye.

Profile of the author

Dr Kathryn Senior is an acclaimed medical journalist who has written over 500 feature articles for leading international journals within The Lancet group. As Senior Writer at Freelance Copy she produces high quality scientific and medical content for websites and printed publications for companies and organisations in the health, medical and pharmaceutical sectors.

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