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Colour blind tests: What are the types of colour blindness?

colour blind eye exam

A colour blind test is a device your optician uses to determine if you have a colour vision deficiency, commonly known as colour blindness.

If you think you might be colour blind, visit your optician. (Don't have one yet? Click here to find an optician near you.)

There are two types of colour blind tests:

  1. Screening tests that can detect the presence of a colour vision problem

  2. More detailed, quantitative tests that can detect a colour vision deficiency and determine the type and severity of colour blindness

Screening colour blind tests

The most widely used screening test for colour blindness is the Ishihara Colour Vision Test.

The test is named after Japanese ophthalmologist Shinobu Ishihara (1879-1963), who devised the procedure and first published a description of it in 1917.

Opticians use Ishihara plates to screen patients for colour vision problems. Someone with a red-green colour deficiency may not see the red number in this example.

The Ishihara Color Vision Test consists of a booklet, each page containing a circular pattern (or "plate") comprising many dots of various colors, brightness and sizes.

The seemingly random coloured dots are arranged in such a fashion that a person with normal colour vision will see a single-digit or two-digit number within the array of dots. But a colour blind person will either be unable to see a number or will see a different number than the one seen by a person with normal colour vision.

The complete Ishihara Colour Vision Test contains 38 plates. Abbreviated versions that contain 14 or 24 plates are more frequently used as screening tests during a comprehensive eye exam.

People being tested generally view the Ishihara plates in normal room lighting while wearing their normal prescription glasses. Because the Ishihara test requires the person being screened to recognise and identify numbers, the test may be less reliable when testing the colour vision of very young children.

A term frequently used to describe the colour images in a Ishihara Colour Vision Test is "pseudoisochromatic plates." This alludes to some of the coloured dots in the pattern that may at first seem equal ("iso-") in colour ("chromatic") with surrounding dots.

But this is a false ("pseudo") sameness, and the difference that exists enables a person with normal colour vision to detect the "hidden" number within the array of dots.

Since the introduction of the Ishihara Colour Vision Test, medical device companies have developed similar colour blindness screening tests using pseudoisochromatic plates.

For example, the ColorDx computerised colour vision test (Konan Medical) is a self-administered, self-scoring app that's available to download on tablet computers.

In addition to testing for genetic colour blindness, the ColorDx app can detect colour vision deficiencies that can develop later in life due to glaucoma, multiple sclerosis, diabetic retinopathy, macular oedema and other disorders, as well as colour vision problems associated with long-term use of medications and other substances, according to the company.

Quantitative colour blind tests

For a more detailed analysis of colour blindness and/or a person's ability to accurately perceive colours, a quantitative colour blind test is needed.

The most popular such test is the Farnsworth-Munsell 100 Hue Test.

The Farnsworth Munsell 100 Hue test identifies and quantifies colour vision problems. (Image: Macular Pigment Research Group, Waterford Institute of Technology)

This test consists of four trays containing many small discs of varying hues. Each tray has a coloured reference disc at one end. The person being tested must arrange the other discs within the tray to create a continuum of gradually changing hue.

For accurate results, the Farnsworth-Munsell 100 Hue Test should be administered in a viewing booth that simulates natural daylight as closely as possible. Also, the coloured discs should be replaced at least every two years to prevent loss of colour saturation that could affect outcomes.

Each coloured disc is numbered on the bottom to enable scoring the results against a key. The closer the match between the test sequence of caps and the correct sequence, the more accurate the person's colour perception is.

In this fashion, the 100 Hue Test can detect whether or not the person being tested is colour blind and also determine the type and severity of his or her colour blindness.

An abbreviated version of the 100 Hue test — called the Farnsworth-Munsell D15 Test — contains only 15 numbered discs of different hues. The D15 test, like the Ishihara Colour Vision Test, is for colour vision screening purposes only, and cannot quantify the severity of a person's colour blindness.

Who should take a colour blind test?

A colour blind test should be given to anyone considering a profession in which accurate colour perception is essential. Examples include electricians, commercial artists, designers, technicians, and certain manufacturing and marketing personnel.

The effect colour blindness has on a person's job performance depends in large part on the colour-related requirements of the position and the severity of the person's colour vision deficiency.

In many cases, fears about being handicapped by colour blindness are unwarranted. Because the condition is present at birth, most colourblind people are unaware of their colour vision deficiency and do not find that it interferes significantly with their daily lives.

Though there is no treatment for colour blindness, in some cases specially tinted contact lenses may improve a colour blind person's ability to perceive the differences between certain colours.

Online colour blind tests

Many colour blind tests can be found online. Most of these are variations of the Ishihara screening test and are presented in varying degrees of quality.

Because exact colour representation is essential for the accuracy of any colour blind test, results from online colour vision screening tests are suspect. For the most accurate results, see your optician and take a colour blind test administered by a trained professional using standardised testing materials under proper lighting.

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