Quantum optics used to measure human eye sensitivity

Nature : Biophysicists have determined that the rod cells in a frog’s eye can detect individual photons, but measuring the sensitivity of the human retina has been limited by the lack of control over how many photons are being sent. Complicating things further, it is estimated that at most 10% of photons entering the eye reach the rod cells in the retina. Now Rebecca Holmes of the University of Illinois at Urbana-Champaign and her colleagues have used quantum optical tools to directly control the number of photons in pulses of light. They fired pulses of 30 photons at test subjects in a dark room. The subjects were able to identify the location of the source of the pulses at a rate that was better than random guessing. Holmes’s team says that because at least 90% of the photons don’t reach the retina, it takes only 3 photons for humans to detect a flash of light.