LogMAR vision chart: This has some advantages over the standard chart and is used in research studies
Ishihara test: This was designed to test for ‘colour blindness’ but is also used as a test for optic nerve disease.
Humphrey field analyzer. This machine is the international standard machine for testing patients’ visual fields.
Your distance vision is measured by comparing yours with that of the average ‘normal’ person. Normal vision used to be known as 20/20 vision; this is now called 6/6 vision. The letters on a Snellen (or logMAR) chart are arranged in lines that become smaller the further down you look.
The first number of your visual acuity measurement refers to how far away you are from the chart, which is generally 6 metres (20 feet) and the second number is the distance from the chart at which a person with ‘normal’ eyesight would see it. So, if your vision is 6/12 this means that you can see, at 6 metres, what a ‘normal’ person can see at 12 metres from the chart. That is, your central vision is half of normal.
Visual acuity in a retinal clinic should be measured with the correct (distance) glasses on, because it is important to know what your best-corrected visual acuity (BCVA) is. Whether you need to wear glasses or not is generally not relevant to retinal conditions.
Near vision is measured using a small handheld chart that has paragraphs of text that is smallest at the top and largest at the bottom. These are of a standard size and ‘normal’ near vision is known as N6, with ‘N’ referring to near and the ‘6’ referring to the size of the letters; N5 is better than N8, for example. You should wear glasses if you need them to read or for close work.
The test simply consists of reading numbers made up of coloured dots of varying colour and size. 13 or 17 colour plates will be tested for each eye.
The standard test (Ishihara) for colour vision was designed to test for inherited colour blindness but is useful for checking whether people have developed problems with colour, as can happen with macular and optic nerve diseases.
Ishihara test This was designed to test for ‘colour blindness’ but is also used as a test for optic nerve disease.
Visual Field Test
This is a test of peripheral vision that is painless and takes about 15 minutes.
The test is done with a machine called a Humphrey visual field analyzer and is difficult for almost everyone the first time, so it often needs to be repeated later to be sure of the result.
The field test is done with you sitting down with one eye covered and a lens in front of your eye if you normally wear glasses to read. With your chin on a special rest and forehead against a strap you will need to keep looking at a spot in front of you. Small dots of light will then flash inside the machine and you should press a button each time you see a light.
The machine will test spots again if it thinks you should have seen them. This is a test of your eye, not you, and you must not worry about whether you have missed a spot. If you remain calm and just press the button when you see a light and look straight ahead all the time it is likely to give a useful result.
If the visual field test is being done to see whether your vision meets the standards required by VicRoads, then the test will be done with both eyes open and you will be allowed to look around if you wish. Your visual acuity will also be tested with both eyes open.