I’ve been chasing details of varifocal contact lenses and I’m sceptical that these work at all. According to this article, the lenses need to actually move on the eye’s surface, which is a dreadful idea.
Instead, today’s invention is contact lenses containing a fluid filled envelope.
As the eye looks ahead, the fluid does not get in the way of incoming rays. Look down, however, and the fluid has an extra refractive effect. This could be continuously attenuated by controlling the radial geometry of the envelope or even by having a fluid which is naturally stratified, providing variable optics.