All humans have the ability to see ultraviolet light, but it is passively filtered out by the eye’s lens. People who undergo surgery to remove the lens can detect ultraviolet light.
Aphakia is the absence of the lens of the eye, due to surgical removal, a perforating wound or ulcer, or congenital anomaly. It causes a loss of accommodation, far sightedness (hyperopia), and a deep anterior chamber. Complications include detachment of the vitreous or retina, and glaucoma.
Aphakic people are reported to be able to see ultraviolet wavelengths (400 nm – 300 nm) that are normally excluded by the lens. They perceive this light as whitish blue or whitish violet. This is probably because all three of the eye’s color receptors are stimulated when a person sees ultraviolet wavelengths (which also happens when a person sees a combination of red, green, and blue light). Some animals, by contrast, have a fourth color receptor for ultraviolet wavelengths (see tetrachromacy). Aphakia might have had an effect on the colors perceived by artist Claude Monet, who had cataract surgery in 1923.
Babies are rarely born with aphakia. Occurrence most often results from surgery to remove congenital cataracts (clouding of the eyes’ lens, which can block light from entering the eye and focusing clearly). Congenital cataracts usually develop as a result of infection of the fetus or genetic reasons. It is often difficult to identify the exact cause of these cataracts, especially if only one eye is affected.
People with aphakia have relatively small pupils and their pupils dilate to a lesser degree.