When you visit your ophthalmologist, you will be asked to perform a number of tests that measure different parts of your vision and look at different parts of your eyes. Some of the tests are very quick and straightforward while others will take more time as they require drops in your eyes to take effect before they can be performed. Some of the tests require you to look at something and respond about what you see. Your ability to perform these tests will depend on your level of vision, and some people may find them difficult or frustrating. Other tests involve the measurement of involuntary responses of the eye or taking photographs of the eye. Some of the tests that are used are explained below. If you have any questions about any of the tests or are unsure of anything taking place during your appointment, don’t be afraid to ask your ophthalmologist or test technician to explain it you.
Visual Acuity Testing
Most people are familiar with visual acuity testing, which involves reading letters from a chart while sitting or standing a certain distance away. The purpose of this test is to measure your central vision which is the ability to see fine detail.
This test measures your colour perception. You will be asked to look at a series of images composed of many small circles. Someone with normal colour vision can recognise numbers within the images.
Visual Field Testing
This test measures the scope or range of vision, including peripheral (side) vision and central vision. A light is brought in from the side on a screen, and slowly moved to the centre of vision. You are asked to press a button as soon as you see the light.
This measures the electrical response of the light-sensitive cells in the eye, the rods and cones. It also measures retinal function. Prior to this test, you will be given drops in your eyes to dilate the pupils. You will also be given an anaesthetic eye drop to numb your eyes. A special type of recording contact lens will then be placed over your eye and electrodes will be placed on the skin near the eye. You will be asked to watch some flashing lights; these are used to stimulate the retina. The electrodes measure the electrical response of the retina to the flashing lights. The test will be performed first in a dark room and then again when the lights are turned on. The test is not painful, but some people may find it uncomfortable. Because of the drops used, you may notice that your vision is blurred for quite some time afterwards.
This test takes a photograph of the retina fundus at the back of the eye using a special camera. The images will show any changes or abnormalities in the back of the eye. You will be given drops to dilate your eyes before this test.
During this test a special dye, called fluorescein, is injected into the bloodstream. The dye is injected through the arm. Its purpose is to highlight the blood vessels in the back of the eye so they can be photographed. This makes it easier for a doctor to see abnormalities in the back of the eye.