The 1.67 may be aspheric, which would alter your peripheral vision slightly. Higher index lenses generally disperse the light more as the index increases, causing more chromatic abberation, especially a problem with high minus lenses.
PD's might be out so you're not looking through the centre of the lens, or the centres may be correct, but the old 1.6 might have been wrong which your eyes have adapted to. This would make the new spex hard to get used to.
Prescription may be wrong or glazed incorrectly.
Go back to the optom who supplied them and explain what's going on.