There is a limit to the amount of charge that your brain can handle. We also know that at that threshold point, there is a laser cascade.
So what would mental strain do that helps the body? Protect it from excess light. I’m sure you’ve gotten mad and seen your vision blur. What is the evolutionary purpose of this mechanism? To reduce the amount of light that hits your brain. Because in the rage state, time slows down. And when time is slow, you would gain more light in the same amount of time. If light is in part the electricity that fuels the body, the eyes would adapt to the new condition by preventing excess light from reaching the brain. If too much light is a bad thing, the body has to have a mechanism to prevent it. And you can’t just blink constantly.
It really doesn’t matter how it works. The truth is that it works. Force your eyes to strain and you see blur. The condition protects your eyes from excess radiation, protects your brain from excess electric charge.
Why would old people not be able to see up close? Farsightedness is a strange and pretty predictable part of aging. The real question is: what is the purpose of it. Essentially, the light is just not focused properly on the retina. According to this theory, the vision problem would actually be a symptom that would help protect them from gaining too much electric charge from the incoming light.
There are all sorts of medical conditions and medications associated with blurred vision. It’s important to think twice about this symptom, because our body strives for equilibrium. And if the vision blurs, it blurs for a reason.