Sight tests, also known as eye examinations, are more than just tests of your vision.

A comprehensive sight test includes a thorough examination of the front and back of the eye for any health problems, too.

You might have certain tests - such as 'auto-refraction' (to provide the optician with a rough estimate of any spectacle prescription) and 'tonometry' (a measurement of the pressure inside the eye) before entering the consulting room.

The optician will ask you questions about any problems you're having with your eyes or might have had in the past, and about any family history of eye problems (some eye problems can be hereditary).

The vision test (known as the 'refraction') includes the use of a letter chart, with different lenses being placed in front of the eye while the optician uses further techniques to fine-tune the prescription.

The prescription is the power of lens for the right and left eye which will correct the patient's vision.

During the eye health check the optician checks the condition of the eye's various structures using an opthalmoscope and a number of other instruments such as a slit-lamp and a visual field analyser.