Sorry to hear your wifes problems. Having suffered from Astygmatism for 40+ years I have no binocular vision at all. Immages in one eye look at a slightly different angle to the other.

A Diopter is a measurement of light displacement through a lens.
1 Diopter means that the lens will focus light at a distance of 1 meter (if I remember correctly) so 10 Diopters means that it will focus light at 0.1mtr or 10cm.
To have a varifocal lens would mean that the lens was not symetrical and focused light at different distances dependant on what part of the lens it passed through!

Best wishes to you and yours....