Sharkey's right about cheap readers. And keep a spare pair in the car.
The other thing is to remember to cut the end of your tippet with scissors or clippers when changing your fly - don't bite it off, that can flatten the end of your tippet and make it harder to thread through the eye. Also have a pin to clear the eye of your fly of varnish.
All difficult things to see when your eyesight isn't what it once was. (You are not alone

)
Try and tie on the fly against a dark background, it shows up the tippet.
If the worst comes to the worst, don't be worried about asking another angler to help you out. The vast majority are only too willing to help.