Nine decades on, a Japanese army doctor’s invention is still being used to test colour vision
Ophthalmology and its related fields of vision care have at their disposal a battery of tests able to assess the health of our eyes and the state of our vision. Many rely on a graphic artefact of some description and of these the acuity chart (or projection) is probably the most common and least remarkable, if only because it is put in front of nearly everyone who visits the optician. Tests for colour vision deficiencies (that is to say, ‘colour blindness’), on the other hand, are less likely to be encountered during a typical visit and so their associated artefacts come less readily to mind. But one test that might be recalled is the ‘Ishihara’, an odd-seeming portfolio of printed disks made up of coloured dots, numerals and squiggly lines.
The Ishihara test is reportedly the most widely used for assessing colour vision, though it is not without its limitations. * As an artefact whose colour accuracy can have a safety-critical dimension, the test itself is often scrutinised for the familiar liabilities of print: colour inconsistency across editions, pigment deterioration over time and the effects of different lighting conditions. Quite understandably, ophthalmologists take these matters seriously. So, too, might designers, since resolving them requires a salutary rigour that is rarely demanded of design and production. But for those who are not already familiar with it, the Ishihara test may also raise a more basic query: simply, why does it look the way it does?
The test is named after Dr Shinobu Ishihara, who was born in Tokyo in 1879 and attended the Imperial University there on a military scholarship. At the request of the Japanese Army, he undertook postgraduate studies in ophthalmology from 1908, first in Tokyo and later in Germany in 1913-14. The outbreak of war in Europe forced Ishihara’s return to Japan where he took up a military physician’s post in Tokyo, and it is at this time that the Army asked him to develop a colour vision test for its conscripts. There were already several such tests in use in Japan, some designed by Japanese ophthalmologists, with another, the ‘Stilling’ test (after the German ophthalmologist Jakob Stilling, first published in 1878) perhaps the most well known.
The principle on which they were based is called Pseudo-isochromaticism. Simply put, it describes the effect of two (or more) colours appearing equivalent (or ‘isochromatic’) when in fact they are distinct (thus ‘pseudo’). This, of course, applies readily to those with colour-deficient vision and can be exploited if colours typically misinterpreted as equivalent are strategically deployed in response- or task-based vision tests that expose the error and so lead to positive diagnoses. If the tests are well considered, they do not require the subject to actually identify colours by name, as this greatly increases the risk of ambiguous answers.
Like his predecessors, Ishihara also based his test on pseudo-isochromaticism, but with the intention of delivering results that were more easily interpreted and thus more reliable. He began with a circular field in which dots of several sizes and tones were evenly though irregularly distributed. They would ensure that within the field no shape larger than the dots (and composed of them) could be discerned either by outline or by tonal changes, since the configuration of the dots would disintegrate these features – a standard camouflage technique. Ishihara could now create shapes within the field that could only be identified on the basis of colour (or, more exactly, hue) alone. This would be done in four ways.
The first involved a ‘transformation’. Two numerals were superimposed in the dot field. Where the numerals overlapped, they were composed of hues that could be distinguished from the background by both normal subjects and by those with colour defective vision. Where the numerals did not overlap, one was completed with hues distinct only to colour normals, the other with hues distinct only to colour defectives. Of the two numerals, the one identified by the subject indicated the state of their colour vision. In some cases, numerals were strategically paired to maximise their overlap (e.g. 8-3, 6-5, 4-1) and so disguise one within the other more effectively. Here, the shared widths and shapes of the clarendon-like italics proved advantageous, as did their swelling strokes and rounded terminals, which settled seamlessly into the field of dots.
On this basis, a further three tests were devised: a ‘vanishing’ design where only subjects with normal colour vision could distinguish numerals in the dot field; its opposite, a ‘hidden’ design where numerals could only be discerned by colour defectives; and a ‘qualitative’ design where differing degrees of numeral visibility helped identify mild or severe disorders. And to ensure that those who were unfamiliar with numerals were not excluded, Ishihara created a second series of tests in the same four ways but which only required subjects to trace paths that meandered around the dot field.
The earliest versions of Ishihara’s test, completed in 1916, were not in fact published but were instead reserved for the exclusive use of the Japanese Army. Nor did they employ numerals initially but Japanese hiragana (and later katakana) characters. Ishihara painted each plate by hand in watercolour and these were translated into print lithographically.
It was not until the following year, 1917, that work was begun to reconfigure the test for use outside Japan. This required Ishihara to dispense with the plates employing Japanese characters, which he replaced with the numeral designs. The new series was named the International Edition, but a publisher could not be found. Undeterred, Ishihara financed an edition of 600 copies himself. Tests for colour-blindness, with sixteen plates and instructions in English, was printed by Handaya & Co. in late 1917, but only a few copies were sold.
In 1921 Ishihara sought to raise the test’s profile by sending copies to universities and ophthalmologists in different parts of the world. Over the next few years, the test gained a measure of acceptance, due in part to favourable evaluations and endorsements from the profession. This in turn led to its adoption for assessing merchant seamen, railway workers and later navy and air force personnel. An accelerating demand also gave rise to a joint publishing arrangement in 1925 between Handaya, who would handle sales of the test in Japan, and Kanehara & Co. who would market and sell the International Edition overseas. (Both publishers are still in operation and their agreement remains in place.)
The test’s increasing popularity necessitated what would become, over the following four decades, a sustained effort by Ishihara to ensure the colour accuracy of each new edition. This proved challenging as a succession of printers took on the work, with mixed results. A scarcity of appropriate papers and colour-fast inks immediately after World War ii made these years understandably difficult. During this period Ishihara, ostensibly retired since 1940, spent a considerable amount of time supervising production. By the early 1960s, however, print quality had stabilised at an acceptably high level, from which it has continued to improve. Today, Ishihara’s tests for colour deficiency, as the book is now titled, is published in three editions of either 14, 24 or 38 plates; the 38-plate edition usually costs more than 0.
Unlike others whose creative, intellectual contributions have gone unrecognised or were only fully acknowledged after assiduous campaigning by others, Ishihara has suffered no such neglect. Near the end of his life, Ishihara was venerated as Bunka Korousyo, a title given to valued contributors to Japanese culture. Since his death in 1963, stewardship of his legacy has been assumed by the Isshinkai Foundation, endowed with the test’s royalties (donated by Ishihara), and tasked with ensuring its high standard of production. In 1984, former colleague Keiu Suda published a monograph that chronicles Ishihara’s 50 years of work on the test (and other aspects of his distinguished career), and to this day his memory is honoured by Japanese ophthalmologists. His original watercolour paintings also survive at the Isshinkai Foundation.
Almost nine decades on from its first edition, the Ishihara test remains widely used, able to quickly screen for colour vision defects that other, more exacting tests can then elucidate in detail. It is thus easy to assert its importance to medical practice in general, and specifically to those for whom a diagnosis of colour-deficient vision offers an explanation for why their perception of the world is often bewilderingly different from others. Ishihara’s test can be celebrated as visual, graphic design of a high order, functionally adept and, in its crafting of colour, form and materials, ineffably Japanese. But beyond these qualities lies a subtler psychological dimension that is also enlightened. It is this: that ‘Ishihara’ is not, finally, a test of mere dysfunction – you either see something or you can’t – but instead one of difference: that (most) everyone sees something, it is just not always the same. This is surely a more productive understanding of colour-deficient vision, and one that guided Shinobu Ishihara to enduring effect.
The Ishihara test can only detect the more common red-green colour vision deficiencies (not the rarer blue ones), and then with only limited precision. A mild form of red-green deficiency occurs when either the red or green sensitive photopigment in the retina has an altered response to colour; this results in reduced discrimination between the colours red and green. A more severe deficiency occurs when either the red or green photopigment is missing entirely.
The plates as reproduced here should not be used for diagnostic purposes. A concise and non-technical discussion of colour-deficient vision and its implications can be found in Donald McIntyre’s Colour blindness: causes and effects (Dalton Publishing, 2002).
Thanks to Dr Mitsuru Sawa (chair, Isshinkai Foundation) and Shoko Mugikura.