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I've had strange eye problems that my doctor hasn't been able to explain, and I feel like my cognition is decliningYou could also explain this with low-level heavy metal exposure, e.g. mercury, as well as a large amount of other possibilities :-)
I thought hard if I should write this, as a joke and only the above line at first, but here it goes. Having read your second paragraph too, that is pretty much exactly what I said to myself a decade ago and before. Then some things escalated a little bit and I was forced to either accept all my increasing issues, or do some research myself.
Turned out I had chronic heavy metal poisoning from mercury. Fortunately diagnosis was made easy because I actually had high levels of it in hair and blood (and urine - same as blood since that's where that comes from). Anyway, the scale of the problem was only made clear during chelation therapy, when both I as well as my (university clinic researcher) doctor were amazed at all the things that improved, including "miracles" such as thyroid normalization (had been enlarged and with a nodule for decades, completely gone within half a year of DMPS chelation, left the endocrinologist speechless, literally, he checked me twice with ultrasound to make sure he had not make a mistake). This issue is next to impossible to diagnose with today's methods, unlike acute poisoning, because how much you see in blood, urine or even hair does not say anything about the size of the problem, it only shows up when it actually moves around the body which it only does after exposure.
I had had dry eyes too, and of course the ophthalmologist as well as I myself attributed it to too much screen work. Today, after years of chelation, I sit in front of a monitor much more than ever before - but now I have zero issues. Same with RSI. Sooo many little things are completely gone from my body, depression too.
The crazy thing is, up to that point ~10 years ago when I had to confront that something was not quite right, I called myself "healthy". And why not? I could run a half marathon just for fun and still come back feeling relaxed. All the many little issues I had, such as a few warts on the feet (more and more over the decades but I ignored the trend), winter depression (many people have that, it's normal!), eye problems (not really severe, so not worth thinking about it) and many many other, my brain refused to think about it. The reality my brain created of my world was highly distorted, but I did not know it. Only the huge and unexpected changes happening after I began chelation (DMPS, later DMSA) showed me the extend of the thus far ignored problem.