Human eye can sense 'invisible' infrared light

A new study has revealed that under certain conditions, it is possible for human eyes to detect the "invisible" infrared light

The international team of researchers co-led by scientists at Washington University School of Medicine in St. Louis has found, by using cells from the retinas of mice and people, and powerful lasers that emit pulses of infrared light, that when laser light pulses rapidly, light-sensing cells in the retina sometimes get a double hit of infrared energy. When that happens, the eye is able to detect light that falls outside the visible spectrum.

Vladimir J. Kefalov, associate professor of ophthalmology and visual sciences at Washington University, said that they are trying to develop a new tool by using what they learned in these experiments, which would allow physicians to not only examine the eye but also to stimulate specific parts of the retina to determine whether it's functioning properly and hope that it would ultimately have some very practical applications.

The idea is that by shining a pulsing, infrared laser into the eye, doctors might be able to stimulate parts of the retina to learn more about its structure and function in healthy eyes and in people with retinal diseases such as macular degeneration.

Although the researchers are the first to report that the eye can sense light through this mechanism, the idea of using less powerful laser light to make things visible wasn't new. The two-photon microscope, for example, uses lasers to detect fluorescent molecules deep in tissues.

The study is published in the Proceedings of the National Academy of Sciences (PNAS).