Although the
polaroid lenses in modern 3D glasses are set with their planes of
polarisation at 90 degrees they are normally both set
diagonally i.e.
/// \\\
/// \\\
This means that even if the glasses are put on the wrong way round the polarisations remain the same. Otherwise the left eye gets the right eye's
image and
vice versa which can lead to
nausea etc. This is necessary as the cheap 3D glasses are normally just flat and the arms bend round (rather than being
hinged) with no clear indication of which side is the
front.
Of course there is still a problem if they are put on upside down but the nose slot should prevent this from happening.