Photosensitizers are chemicals that absorb photons and use that energy to promote electrons to higher energy states, and typically those activated electrons produce free radicals that react with other substances in the cell. That’s not particularly scary: your eyes contain proteins, opsins, and a chemical, retinal, that also absorb photons and use the energy to cause a conformational change in retinal. But photosensitizers are also used in cancer therapy. Load up a tumor with photosensitizers, then shine a laser on it, and all the free radicals do a bang-up job of destroying the cells, exactly as you want.
That’s probably not what you want to have happen in your retina. Photosensitizers can be used there, too, and they can act as extra light absorbent pigments that might eventually, you hope, transfer their energy to signal transduction pathways. You couldn’t pay me enough to let anyone try that kind of experiment on my eyes, though.
But someone has been crazy enough to try. Gabriel Licina has been doing the kind of citizen science I’d normally approve, except in this case, he’s putting risky drugs in his eyes for a small and temporary enhancement. That’s crazy!
He’s using a solution of a photosensitizer called Chlorin e6, which is normally used in cancer therapies as described above. A lot of the media reporting on it is getting all squicky about him “injecting” it into his eyeball, which is not true: he’s just applying it as eye drops. The media seem less freaked out by something else that bothers me a lot: for the photosensitizer to be effective, it has to get to photoreceptors in the retina, which just applying to the surface of the eye won’t do — so he adds DMSO.
DMSO is a useful but dangerous chemical: it passes right through cell membranes, carrying along whatever is in solution with it. Everything in that vial of solution is getting transported into his eyes and his bloodstream. I’ve used it in some fixatives, and I’ll tell you, a solution of DMSO plus nasty chemical is something you treat with respect and fear. I wouldn’t touch it with my hands, let alone put it in my eyes.
Apparently, Licina’s experiment worked, the Chlorin e6 was absorbed into his retina, and he experienced enhanced night vision for a few hours. The military is probably quite happy to hear that, especially since they didn’t have to pay for it, and didn’t have to pressure any ‘volunteers’ to submit to it.
Lawyers might be unhappy. Who is Licina going to sue if there are long term detrimental effects?
This was a high risk, low payoff experiment. Don’t do these sorts of things! He has put his vision at risk, and all for a few hours of slightly better vision in the dark and a relatively worthless ‘publication’ on a website that might inspire a few more stupid young people to do chemistry experiments on their eyeballs.
I should also point out that this experiment is one that could not be done in a real university — it fails ethically, has potential side effects that would need to be studied in animal models first, and would never pass a review board. But apparently, to some people, the fact that ethical scientists would never do that is a point in its favor.