Colour vision deficiency

Japanese ophthalmologist and Professor at the University of Tokyo, Shinobu Ishihara (1879-1963) developed his colour vision deficiency test, first published in 1917, to test for colour anomalies in human vision. His collection of 38 plates (known as pseudisochromatic plates) consist of arranged coloured spots, varying in size, colour saturation and brightness, within which are numbers or lines.

Visible to people with normal colour vision, the patterns are difficult to detect by those with ‘colour blindness’. Approximately 8% of Caucasian males suffer from the most common type of deficiency, which is an inability to differentiate between red and green hues. As this condition is linked to genes on the X chromosome it is much more common in men than women, as men have one X chromosome, compared to two in women. Less than 1% of women have the red-green deficiency.

Ishihara’s test determines whether an individual has colour perception difficulties, based on the lack of light absorbing pigments within the retina. These photoreceptors are known as cones and if their spectral sensitivity to short, medium or long light wavelengths is altered or lost, then it will cause a limitation in recognising hues accurately, particularly when discerning colours similar in saturation or brightness.

Colour recognition is an often neglected component of professional design (graphic, product, directional, informational) and should be considered as essential when forming concepts and structures that require clear definition and easy recognition, regardless of actual colour. Attention must be given to creating elements with high contrast, non-similar saturation, and variation of shape and form – something that will also aid definition and readability for people with normal colour perception too.

Various design resources are available online to assist this process, with one of the best being the free program Color Oracle, which simulates how a colour deficient viewer will perceive your work. This software can be easily applied to any available design, highlighting areas of concern and aiding the designer to produce results not solely reliant on correct colour perception.

Below are four of Ishihara’s 38 plates – can you read the numbers?

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