If my vision has gotten noticeably worse, to the point of near blindness, is that a concern for medical separation?

If your eyesight, while poor, is correctable to acceptable limits, then don't worry. I'm near sighted...with it being pretty bad on the distance vision. I can't clearly see the ONE GIANT LETTER at the top of the chart without my glasses. It's just a giant black fuzzy haze. My glasses put me at 20/20 to 20/15. So, again, relax young Padawan. Worrying about this is like sitting in a rocking chair. It gives you something to do but you aren't going anywhere.

PFC (Join to see), as the saying goes, "Don't borrow trouble" - don't worry about something until you have something to worry about.

Get your eyes checked out by an optometrist and/or ophthalmologist - it could be just a case of your eyes getting worse normally.

The military doesn't separate you once you're in because you have correctable poor vision. If you were not able to correct the vision through glasses, that might be an issue (depending on how bad the vision is).

Of course, your career as a pilot or professional lifeguard might have to change...

Yes, it could be an issue if it isn't correctable and/or is getting worse. Read through AR 40-501, specifically Chapter 3. Keep in mind that while you don't want to report your concerns, your vision may place your fellow troops in danger.