How can you tell the difference between right and left contact lenses?
As such there is no difference between the lenses as long as
prescription is same for both the eyes.
So in mostly both the eyes have same prescription.
If there's a difference, then mark the case with some indicators
to distinguish.
When you are getting your contact lens prescription the first
time, the eye doctor will mark the box for you if you have a
different precription for each eye. L means the contact lens will
go in the left eye and R will go in the right eye.