I have used the magnifiers for tying on flees... useful.
Alternatively... the last couple of outings i've re-discovered using the C&F fly threaders for getting small flies onto the tippet - definitely worth a try for overcoming fading eyesight. I thread a few flees onto a threader before leaving the house, then it's easy to transfer them onto the tippet even in the gloom. You've still got to tie the knot on the fly mind you, so it's not the total solution!
i,