Check your colour vision deficiency

Ishihara Test for Color Blindness is designed to provide a test which gives a quick and accurate assessment of color vision deficiency of congenital origin (colour blindness).

Types of colour blindness

Most cases of congenital color vision deficiency are characterized by a red-green deficiency which may be of two types;

• Protan type which may be complete (protanopia) or partial (protanomalia) -  the visible range of the spectrum is shorter at the end compared with that of the normal, and that part of the spectrum which appears to the normal as blue-green, appears to those with protanopia as grey. The whole visible range of the spectrum in protanopia consists of two areas which are separated from each other by this grey part. Each area appears to those with protanopia as one system of color with different brightness and saturation within each area, the color in one area being different from that of the other. The red with a slight tinge of purple which is the complementary color of blue-green appears also as grey. 
• Deutan type which may be complete (deuteranopia) or partial (duteranomalia). 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 protanomalia and deuteranomalia, there is not part of the spectrum which appears grey. But the part of spectrum which appears to those with protanopia as grey, appears to those with protanomalia as a grayish indistinct color, and likewise, the grey part of the spectrum seen by the person with deuteranopia appears to those with deuteranomalia as a 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. The application of this peculiarity to the test for color vision deficiencies is the distinguishing feature of this series. 
• In the congenital color vision deficiencies, although very rare, there is total color weakness. The color sensitivity of the total color weakness to red and green, as well as to yellow and blue is very low and only the clear colors can be perceived; but, except for the color sensitivity, there is no abnormality in the visual functions.
• There is also a very rare group of persons who suffer from total color blindness and show a complete failure to discriminate any color variations, usually with an associated impairment of central vision with photophobia and nystagmus. Furthermore, a failure in the appreciation of blue and yellow may be termed tyritanomalia if partial, and tritanopia if complete, but, even if such cases do exist, they are extremely rare. 

How to use the test

The test consists of identifying the numbers in different colour plates. It is an easy method of establishing the diagnosis of colour blindness and in distinguishing them from cases of red-green deficiencies.

There are different plates that are designed to be appreciated correctly in a room which is lit adequately by daylight. The introduction of direct sunlight or the use of electric light may produce some discrepancy in the results because of an alteration in the appearance of shades of color. When it is convenient only to use electric light, it should be adjusted as far as possible to resemble the effect of natural daylight. It is important that the test plates should not have a fading of the color of the plates.

The plates are held 75 cm. from the subject and tilted so that the plane of the paper is at right angles to the line of vision.The numerals which are seen on plates are stated, and each answer should be given without more than three seconds delay.

It is not necessary in all cases to use the whole series of plates. Plates 12, 13 and 14 may be omitted if the test is designed merely to separate the color defectives from those with normal color appreciation.

To access the colour plates, click here.

Explanation of the plates

• No. 1. Any subject, whether with normal or defective color vision will read correctly the figures “12”. This plate is used mainly for preliminary explanation of the test process to the subjects.
• No. 2. Normal subjects will read “8” and those with red-green deficiencies “3”.
• No. 3. Normal subjects will read “5” and those with red-green deficiencies “2”.
• No. 4. Normal subjects will read “29” and those with red-green deficiencies “70”.
• No. 5. Normal subjects will read “74” and those with red-green deficiencies “21”.
• No.6-7. Correctly decipherable by normal subjects, but illegible or hard to read for those with red-green deficiencies.
• No. 8. Clearly “2” for normal subjects but obscure for those with red-green deficiencies.
• No. 9. Normal subjects can hardly read it, but most of those with red-green deficiencies see the figure “2” in it.
• No. 10. Normal subjects can usually read the figures “16”, but most of those with redgreen deficiencies cannot.
• No. 11. In tracing the winding line between the two x’s, the normal trace the bluishgreen line, but the majority of those with color vision deficiencies are unable to follow the line or follow a line different from the normal one.
• No. 12. Normal subjects and those with mild red-green deficiencies see the figures “35” but protanopia and strong protanomalia will read “5” only, and deuteranopia and strong deuteranomalia “3” only.
• No. 13. Normal subjects and those with mild red-green deficiencies see the figures “96” but protanopia and strong protanomalia will read “6” only, and deuteranopia and strong deuteranomalia “9” only.
• No. 14. In tracing the winding lines between the two x’s, the normal trace along the purple and red lines.
• In protanopia and strong protanomalia only the purple line is traced, and in case of mild protanomalia both lines are traced but the purple line is easier to follow.
• In deuteranopia and strong deuteranomalia only the red line is traced and in case of mild deuteranmalia both lines are traced but the red line is easier to follow.

Analysis of the results

As assessment of the readings of plates 1 to 11 determines the normality or defectiveness of color vision. If 10 or more plates are read normally, the color vision is regarded as normal. If only 7 or less than 7 plates are read normal, the color vision is regarded as deficient. However, in reference to plate 9, only those who read the numerals 2 and read it easier than those on plate 8 are recorded as abnormal. It is rare to find a person whose recording of normal answers is 9 or 8 plates. An assessment of such a case requires the use of other color vision tests, including the anomaloscope.

Source : Ishihara Instructions - The Series of Plates

Related resources

• Digital Ishihara Test for Color Blindness