When I was a postdoc at berkeley I was talking to a professor (chair of my department) and he said he had done some research on this problem (if you watch the movie Right Stuff, one of the guys who goes to space may experience this due to cosmic gamma rays).
The professor said something that I still think is audacious. He wanted to resolve the issue, but couldn't get IRB approval to run experiments on students, so he experimented on himself. By looking into a synchrotron. Synchrotrons are some of the most powerful lights humans make, with broad spectrum and extremely high intensities.
He said he did a bunch of calculations to come up with filters to ensure that statistically a very small number of photons with specific energies entered his eyeball. Installed those into the viewing platform on the synchrotron, and opened the aperture with his eye in the light path.
>Abstract
Hypothesized that light flashes observed by astronauts in space are caused by ionization or another form of interaction of primary cosmic particles with tissues, and that "streaks may be heavy primaries, and double points could be accounted for by 1 cosmic particle intersecting the retina at 2 points . . . . To test the validity of these hypotheses and the probability that the human dark-adapted eye may be a sensitive and unique cosmic ray detector," visual phophene phenomena produced by fast neutrons were investigated using 2 human Ss. Ss "were exposed to a beam of fast neutrons with energies between 20-640 MeV produced by a 0.64 GeV proton beam impinging on a 12 cm beryllium target." Both Ss were dark adapted over 2 hr. before exposure. After exposure, 1 S saw pinpoint flashes coinciding with the presence of the beam; the other S saw between 25-50 bright discrete lights. In another exposure in which the beam contained no protons or other particles, there were no observations of visual phenomenon during or after a total exposure of about 5,000 particles through each retina. X-ray phosphenes did not produce visual phenomena similar to bright pinpoints of light observed during neutron exposure. It is suggested that if the passage of "particles causes irreversible deterioration of retinal cells and of neurons, then in a long space flight outside the Earth's magnetosphere, a significant degree of random cellular damage might result." (PsycINFO Database Record (c) 2016 APA, all rights reserved)
The professor said something that I still think is audacious. He wanted to resolve the issue, but couldn't get IRB approval to run experiments on students, so he experimented on himself. By looking into a synchrotron. Synchrotrons are some of the most powerful lights humans make, with broad spectrum and extremely high intensities.
He said he did a bunch of calculations to come up with filters to ensure that statistically a very small number of photons with specific energies entered his eyeball. Installed those into the viewing platform on the synchrotron, and opened the aperture with his eye in the light path.
I believe it's this paper (currently paywalled): https://www.nature.com/articles/230596a0 which should describe the experiment and the identity of the subject.