Testing for Color Blindness

November 12, 2012

Testing for Color Blindness

There are some professions where testing for color blindness is necessary, e.g. electricians. It is crucial to be aware of the correct colors as it affects safety. The nature of the role you carry out and the importance color related issues play may mean there is little or no effect in you carrying out your job.

As color vision defects are present at birth many people are totally unaware of their condition and do not find it gets in the way of their everyday life. There is no cure for color blindness but there are contact lenses which have special tints and they may help to differentiate certain colors.

Your doctor can carry out two color vision tests to ascertain whether you have this color vision defect. The Ishihara Color Vision Test is a screening test which identifies if a color vision problem is present and is named after Shinobu Ishihara (1879-1963) who was an ophthalmologist. He conceived this method and the report was first published in 1917. This test involves looking at a booklet which has a circular pattern (or plate) consisting of many dots in varying colors, sizes and brightness. At first sight, it may appear random but the colored dots are organized in a way that someone with normal color vision will see either a single or two digit numbers within the collection of dots. Someone who is color blind will not be able to see any number or they will see a completely different one than a person who has normal color vision. Ophthalmologists will use Ishihara plates to test patients with color vision deficiencies, e.g. if it is a red-green deficiency the patient may not see a red number. Thirty eight plates are included in the complete Ishihara Color Vision Test and the shortened test includes fourteen or twenty four plates. The shortened test is often used as a screening test when taking part in a full eye examination.

The second test is a quantitative color blind test to identify a color vision problem and this test allows the seriousness and the nature of the color blindness to be identified. Farnsworth-Munsell 100 Hue Test is established and involves four trays which include small disks of different shades and tones. A colored reference disk is located at one end of the tray and the person who is being tested has to organize the disks in the tray to produce a range of the varying changes of the shades and tones. To achieve perfect results, the Farnsworth-Munsell 100 Hue Test should be carried out in a cubicle where natural daylight can be reproduced. In order to work effectively the colored disks should be replaced every two year at least.

The colored disks are numbered to allow scoring of results alongside a key. To determine the accuracy of the color perception of the person, the test requires them to match up the test sequence of caps and the correct sequence. By doing the 100 Hue Tests it confirms whether color blindness is present, the severity and the type of color blindness. There is a shortened form of the 100 Hue tests which is called Farnsworth-Munsell D15 Test and this has 15 numbered disks of various shades and tones. Similar to the Ishihara Color Test, this D15 test cannot identify the seriousness of the color blindness; it is only for color vision screening.

Color blind tests are available on the internet. These tests are usually based on the Ishihara screening test. The quality of the test varies greatly and they should not be seen as a definitive diagnosis of color blindness. If you have any concerns about color blindness, arrange an appointment with your eye doctor and request a color blind test with the correct lighting and proper equipment.


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