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It is fairly common knowledge that the lens in its normal state absorbs ultraviolet (UV) radiation. An interesting notion has come up from time to time in my reading that suggests there are a small number of conditions that result in humans being able to 'see' ultraviolet.

What conditions may cause this? Also, those affected, would they 'see' it has a different shade of violet?

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up vote 11 down vote accepted

You will be interested in Aphakia, which is the lack of an eye lens usually through surgery but sometimes from birth. These individuals supposedly see UV as a whitish-blue or whitish-violet:

This appears to be because the three types of colour receptor (red, green and blue) have similar sensitivity to ultraviolet, so it comes out as a mixture of all three - basically white, but slightly blue because the blue sensors are somewhat better at picking up UV.1

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