Some birds can see ultraviolet light, so can some reptiles and plenty of insects. However mammals couldn’t, until now. Recent research has found that the Reindeer can see Ultraviolet, which is really a first. Why though is a different question.
There is a definite reason why mammals cannot see ultraviolet and it is safety. Mammals tend to life for relatively long times, so can’t risk damage to body parts. Ultraviolet damages eyes, although it is useful it is harmful. Some species of Falcon live for 15 years and use Ultraviolet to look at trails left by prey, if they lived any longer they wouldn’t be able to because simply, their eyes wouldn’t work. The problem is the energy Ultraviolet light contains.
Ultraviolet is light with a shorter wavelength than our normal visible light spectrum, and so it has much more energy. It is the stuff which can cause skin cancer. That suncream/sun block you use. It is stopping that Ultraviolet light bursting through our skin, damaging cells and messing up your DNA. It is however, possible to see ultraviolet in extreme cases. When people have their cornea replaced, if there is a fault then the cornea might not filter out these ultraviolet light, so they can see any source of ultraviolet lights. This is not just harmful, it is actually painful to look at any source.
Taking all of that into account it is especially amazing that Reindeer can both stand it, and make sense of a whole new type of light. Their eyes must have a new kind of protection, or maybe science is wrong. All we know is that they can see it, it is useful for them, and we don’t quite know how they are doing it. Oh well.