What types of test are there for colour blindness?
There are several different colour vision tests you can take to see which colour vision impairment you have and the condition's severity. None of them are invasive and shouldn't take too long to complete before a diagnosis can be given.
Colour vision impairment is usually inherited, although it can result from exposure to chemicals, the use of medications or some diseases and illnesses. The eye contains a light-sensitive layer of tissue called the retina and it has cells that enable you to interpret colours. These cells, known as cones, have three types - blue, green and red. If a certain type of cone is missing or not working properly, this causes colour vision deficiencies. When inherited, the condition is far more common in men than in women, and usually results in problems distinguishing reds and greens. If colour impairment is the result of an underlying health problem, blues and yellows tend to be the colours people struggle to define.
The Ishihara Colour Test
Arguably the most recognisable colour vision exam is a test designed by Japanese professor Dr Shinobu Ishihara nearly 100 years ago. The test consists of various plates - known as Ishihara plates - that contain circular dots of different shapes, sizes and colours. Within the pattern, there is a number or shape that is clearly visible to those that have no colour vision deficiency and invisible or difficult to see for people with red-green colour blindness. Some of the plates work the other way around. There are also certain diagnostic plates that are used to determine which type of colour deficiency is prevalent and its severity. The full test is 38 plates, although some are only 24 plates, and colour impairment is usually obvious after just a few plates.The HRR Colour Test - named after its creators Hardy, Rand and Rittler - uses a similar method, but also includes a diagnosis for blue-yellow deficiencies.
Farnsworth-Munsell 100 Hue Test
Developed by Commander Dean Farnsworth in the 1940s, this test requires participants to arrange 100 colour hues in a row. The aim is to have the colours in a natural order so that they change gradually as you look left to right. The test is typically ordered in four rows of 25 hues, with the first and last tile of each row locked in place to serve as a guideline. The Farnsworth-Munsell 100 covers orange-magenta, yellow-green, blue-purple and purple-magenta hues. This offers comprehensive results that can detect minute colour deficiency problems. The test used to be conducted using physical tiles that you moved into place, but it is now easy to do via a computer.Aside from identifying severe colour deficiencies, it is also popular in the design world where small discrepancies in defining hues could impact work quality. Farnsworth is also known for developing the Farnsworth Lantern Test, which was a simpler colour impairment exam given to US military personnel. It allowed for a 30 per cent colour deficiency, enabling people who were not severely impaired to still serve.