Are these you first varifocals? The fit of the lenses in varifocals is more critical than ordinary lenses as the centre of each lens needs to be aligned accurately with the eye. Twice now, once by Boots and once by Specsavers, I've had to have the lenses replaced, both times with no fuss. It seems that I hold my head more upright than many people but, when having the new frames measured for the lenses, they get me to look at an unusual angle (if that makes sense).