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Super seers: why some people can see ultraviolet light

4 December 2019

I have heard that it is possible for some people to see ultraviolet light. Is this true, and if so, how is it possible?

Richard Swifte Darmstadt, Germany

The human retina is sensitive to the ultraviolet (UV) spectrum down to about 300 nanometres, but the lens of the eye filters it out. This adaptation perhaps arose to protect the retina from the more damaging UV. It also avoids the increased blurry effect of having too wide a spectral range, since different wavelengths focus at different distances from the lens.

Artificial lenses are designed to block UV. But people born without a lens, or who have a lens removed and not replaced, sometimes report seeing ultraviolet as a whitish-violet light. One example is the Impressionist painter Claude Monet, who developed bad cataracts in later life and eventually had his left eye’s lens removed. His subsequent works heavily feature bluish colours, often thought to be the result of him seeing UV.

Brian Horton West Launceston, Tasmania, Australia

Normal colour vision ranges from wavelengths of around 380 nanometres (violet) to 750 nanometres (red). Most people can’t easily see light shorter than 380 nanometres because the lens of the eye absorbs it. If the lens is missing or removed, often due to cataracts, light below the violet range isn’t blocked and can be detected down to around 310 nanometres. Without the lens to focus light, these people are far-sighted and need corrective lenses to focus at short distances.

Insects can see ultraviolet light, and some other animals have vision in this range too.

Bob Butler Llangoed, Anglesey, UK

Some years ago, after being admitted to hospital with sepsis, I developed uveitis, an eye inflammation that could have caused permanent loss of vision. The lens of my right eye was removed and replaced with an artificial one. The new lens meant I could see better through this eye than I ever had before.

On leaving hospital, I decided I deserved a pint of bitter. Standing at the bar of my local pub, I noticed that their device for detecting counterfeit banknotes was emitting very bright bluish light. I mentioned this to the barman, who looked at me with a very quizzical expression but made no comment. I then realised that he couldn’t see the light: it was visible through my right eye alone.

It seems that the natural lens in the eye has a filtering effect as a protection against ultraviolet light. I owe the staff of the emergency eye clinic my thanks not only for saving my eyesight, but also for my ability to see UV light.

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