The best we can do is fight a delaying action against the ravages of time...
Here are some things that have helped me along the way:
1) You can get cheap ($2-5), high magnification (usually up to 4X) half-lens readers that you can buy several of so you won't mind losing them or scratching them up over the course of a season. Wally World is a decent source and (surprisingly..) you often find the most durable and higher mag models at some of the "Dollar"-type stores. I've sued these as is and I've also slipped them inside my prescription bifocals to get even more.
magnification.
2) As Tom mentioned, light matters. But it isn't the same for everyone... I have as much trouble in bright sun as I do in heavy shade. Move around until you find your best light level.
3) If you tie (and particularly if you are a sloppy tier like me..), pay more attention to making sure you leave a clean eye unclogged by errant cement, thread or wisps of hackle.
4) For me anyway, it is much easier to manage small dry flies that are tied on straight eye hooks. Pretty much all my dries that are #16's or smaller are on these hooks. Then see #3...
5) The smallest size blue plastic floss threaders that come 80-100 to a package for a couple bucks work great on #14 and larger flies if you are having trouble in that range. Just thread your tippet through the loop in floss gizmo and then stick the post of the thing through the hook eye. Pull though. Viola! or Wha La! or however you want to spell it.. These things also work well to open up the vent holes in hearing aid ear molds so the devices don't feedback and whistle. But you didn't ask about that.. They also work well as bobbin threaders at the tying bench and will bake your $4 bobbins last a lot longer. But you didn't ask about that either...
That's all I know..