So, as I understand it there are three main spots on the body where COVID infection typically takes place -- the nose, the mouth, and the eyes. It is relatively easy to obtain a very protective mask for the nose and mouth (n95/p100), but a large majority of people seem to be using masks that do not provide eye protection. How much extra protection can be gained by protecting your eyes?
(Obviously, the degree of protection one might use can vary -- on the low end we might have "wear glasses", while then we might progress further with things like "disposable face shield over mask", "wear a full face respirator rather than nose/mouth only", and then even "full head positive pressure hood" on the very high end.)
To be honest, my impression was that it was well known that the eyes were a potential infection route and that this didn't need much other evaluation -- as I understand it risk of infection via rubbing the eyes was one of the main reasons that "don't touch your face" was such prevalent advice early on.
I believe there are studies indicating glasses-wearers have a reduced infection risk (though obviously lots of potential confounds there), that face shields reduce risk if worn with a mask (though some of this may be blocking particles from making direct contact with a mask/filters), etc. but have not done an in-depth evaluation of that topic.