What is it?
When an optometrist, or optician, gives you a sight test, their examination will include refraction. Refraction is that part of the test which checks the health of your eyes and finds out what kind of glasses will correct or assist your vision. If you are a patient in a hospital and are sent for refraction it will be purely to identify the glasses you need.
When is this test carried out?
Refraction is done when the ophthalmologist wants to know if your vision can be improved, for example, after a cataract operation when your glasses are likely to need changing. A refraction can also help the ophthalmologist decide whether or not to operate. If new glasses alone can improve the vision, then an operation may not be immediately necessary.
What does it offer?
A refraction will show if your vision can be enhanced with glasses. It can also reveal any changes in the eyes, such as the development of cataract.
What happens during the test?
You will be asked to read a letter chart a few metres away. This will most likely be the very familiar Snellen chart, which has rows of letters decreasing in size from the top of the chart to the bottom. Your level of vision is measured by the smallest line of letters you can read from a distance of six metres. For younger children these charts can be modified so that they use pictures instead of letters, or the child may be asked to match a single letter to one they are holding themselves.
You will also be asked to read from a page of print. This will have paragraphs with different sizes of text. Small children may be shown pictures of different sizes to name.
The optometrist will then ask you to put on a trial frame. This is a special sort of spectacle frame that can hold the different lenses so that the optometrist can check which ones offer you the best vision. Whilst you are wearing the trial frame you will be asked to look in a certain direction while a light is shone into your eyes. After this you will be shown different lenses and asked which ones make your vision clearest.
Younger children may not have to wear the trial frame and they may also need to have “dilating drops” put in before the refraction is done.