Color Vision Test

The importance of color vision testing

It is important to know if you are colour blind. Colour is often used as an aid to teaching in pre-primary and primary schools. Children who have difficulty distinguishing between colours may be misdiagnosed as having learning difficulties unless it is known beforehand that they have a colour vision defect. Knowing the existence of a colour vision defect early can thus help prevent communication problems in school and in later adult life.

Schoolchildren with colour vision defect should think over carefully before choosing study subjects where colour discrimination is important. Art and chemistry are two examples of such subjects.

Consider colour deficiencies when making career decision. This is because many occupations demand good colour discrimination. Defective colour vision is a handicap in some pharmacy and chemistry jobs. Colour is often used to convey important information such as in traffic and navigational lights and colour coding of electrical wires.

How we see color

Our eyes are capable of differentiating an infinite array of colours. Yet, would you believe that all our colour sensations are actually derived from varying stimulation of only three types of colour receptors, namely red, green and blue?

These receptors, called cones, are found solely in the centre part of the retina in an area called the macula. The retina is the nerve layer lining the back of the eye, much like the film in a camera.

The colours red, green and blue are also known as the primary colours. A suitable mixture of these three colours can produce any colour including white!

Ishihara Color Vision Test

The Ishihara Color Test is an example of a color perception test for red-green color deficiencies. It was named after its designer, Dr. 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 visible to those with normal color vision and invisible, or difficult to see, for those with a red-green color vision defect. The full test consists of 38 plates, but the existence of a deficiency is usually clear after a few plates. Testing the first 24 plates gives a more accurate diagnosis of the severity of the color vision defect.

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; the first testing for protanopia and the second for deuteranopia.