In old times, there was no proper way of testing the eyes of any person. Any sightedness was very difficult to detect as there wasn’t any equipment or any method to do so.
Similarly, color blindness also remained undetectable until recent times. However, with the increasing number of cases, it became necessary to invent ways and equipment to counter such problems.
In the textile, apparel and fashion design field, communication, specification, and identification of color is very important. The people who are involved in any process related to color should be able to identify colors because the color is a highly visible phenomenon of significant importance to product outcome as well as the customer.
The Ishihara test is a color perception test for red-green color deficiencies, the first in a class of successful color vision tests called pseudo-isochromatic plates (“PIP”). It was named after its designer, Shinobu Ishihara, a professor at the University of Tokyo, who first published his tests in 1917.
The test consists of a number of colored plates, called Ishihara plates, each of which contains a circle of dots appearing randomized in color and size. Within the pattern are dots which form a number or shape clearly visible to those with normal color vision, and invisible, or difficult to see, to those with a red-green color vision defect. Other plates are intentionally designed to reveal numbers only to those with a red-green color vision deficiency and be invisible to those with normal red-green color vision. The full test consists of 38 plates, but the existence of a severe deficiency is usually apparent after only a few plates. There are also Ishihara tests consisting of 10, 14 or 24 test plates.it’s the most widely used color perception test for such deficiencies.
You can test yourself online using the below link.
How the Ishihara Test Works
- It is a color perception test that uses 38 plates in order to detect red-green color deficiencies. It is also called as ‘38 plates CVD test’. There are several types of plates that are given to the person under test.
- Each of the plates consists of a circle of dots that appear to be randomized in color and size.
- Some plates contain a number which is visible to the person with normal eyes and invisible or very difficult to the person with red-green color deficiencies.
- Other plates contain numbers that are visible to the person with deficient eyes and barely visible to those with normal eyes.
- The results extracted from plate observations define the person as normal or deficient. Normally, a severe deficiency can be detected after a few plates and a little deficiency may require all plates to be categorized accordingly.
Types of Plates
There are four different types of plates:
Transformation plates: A different color will be visible for a normal person than the color deficient ones. Color-blind people will see a different sign than people with no color vision handicap.
Vanishing plates: The figures on these plates will be visible just for the persons with normal color vision. If you are color blind you will not see anything.
Hidden digit plates: Only color-blind people are able to spot the sign. If you have perfect color vision, you will not be able to see it.
Diagnostic plates: These are purposely built to detect the severity of the deficiency and the type of it (protanopia or deuteranopia).This is used to differentiate between red- and green-blind persons. The vanishing design is used on either side of the plate, one side for deutan defects an the other for protans.
In deuteranopia, that part of the spectrum which appears to the normal as green appears as grey, and the visible range of the spectrum is divided by this zone into two areas, each of which appears to be of one system of color. The visible range of the spectrum is not contracted, in contrast to protanopia. Purple-red which is the complementary color of green appears also as grey.
In protanopia and deuteranopia, there is not part of the spectrum which appears grey. But the part of the spectrum which appears to those with protanopia as grey appears to those with protanopia as a grayish indistinct color, and likewise, the grey part of the spectrum seen by the person with deuteranopia appears to those with deuteranopia as an indistinct color close to grey. Consequently, one of the peculiarities of red-green deficiencies is that blue and yellow colors appear to be remarkably clear compared with red and green colors.
Test Method and Environment
- The plates are designed to be assessed in a room that is lit adequately by daylight or artificial lamp close to daylight.
- Plates should be held at a distance of 75 cm from the subject and tilted so that the plane of the paper is at right angles to the line of vision.
- The plates 1–25 should be read within 3 seconds.
- If the person is unable to read the numerical, plates 26–38 are used and the winding lines between the two ‘X’ are traced with the brush.
- Each tracing should be completed within 10 seconds.
- An assessment of the readings of plates 1–21 determines the normality or color vision defect.
- If 17 or more plates are read normally, the color vision is regarded as being normal.
- If 13 plates (or less) are read correctly, the color vision is regarded as deficient.
- Testing with the first 24 plates gives a more accurate diagnosis of the severity of the color vision defect.
- Ishihara color plates nos. 4, 6, 10 and 16 read as numerical 29, 5, 2 and 16 respectively by a normal observer.
- Common plates include a circle of dots in shades of green and light blues with a figure differentiated in shades of brown, or a circle of dots in shades of red, orange and yellow with a figure in shades of green.
Explanation of The Plates
As assessment of the reading of plates 1 to 21 determines the normality or defectiveness of color vision. If 17 or more plates are read normally, the color vision is regarded as normal. If only 13 or less than 13 plates are read normal, the color vision is regarded as deficient.
- However, in reference to plates 18, 19, 20, and 21, only those who read the numerals 5, 2, 45, and 73 and read them easier than those on plates 14, 10, 13 and 17 are recorded as abnormal.
- It is rare to find a person whose recording of normal answers is between 14-16 plates. An assessment of such a case requires the use of other color vision tests, including the anomalscope.
- In the assessment of color appreciation by the short method involving 6 plates only as described on page 4, a normal recording of all plates is proof of normal color vision.
- If there is a discrepancy in any of the recordings, the full series of plates should be used before diagnosing a red-green deficiency.
S. Ishihara, Tests for color-blindness (Handaya, Tokyo, Hongo Harukicho, 1917). Kindel, Eric. “Ishihara”. Eye Magazine. Retrieved 3 December 2013. Fluck, Daniel. “Color Blindness Tests”. Colblinder. Retrieved 3 December 2013. “Whonamedit – dictionary of medical eponyms” www.whonamedit.com. Retrieved 12 August 2015. www.dfisica.ubi.pt/~hgil/p.v.2/Ishihara/Ishihara.24.Plate.TEST.Book.pdf www.colorblindness.com/ishihara_cvd_test/ishihara_cvd_test.html