Actually, it is completely possible to make glasses with and without
monovision for this kind of anisometropia.  What is true is that often
such glasses cause binocularity problems (not always), which is why most
vision insurance plans will pay for "medically necessary" contacts when
the aniso (difference) is over 2 D. or so.

w.stacy, o.d.

I've read that wearing contact lenses is the only option when there is
a significant disparity in uncorrected vision between the eyes (say -1D
right eye and -5D left eye).  Would it be possible to make monovision
glasses that might work without the contact lenses?