Cauchy dispersion formula

Hi everybody,

I would like to use the 'cauchy dispersion formula', ie (http://en.wikipedia.org/wiki/Cauchy's_equation):

eta = A + B / w²

Where :
eta is the resulting IOR
A is the base IOR
B is the dispersion coefficient expressed in squarre meter (m²)
w is wavelength expressed in micro-meters

I try to apply this formula this way :
B = 0.013 in micro-meters,
A = 1.72

So first,
1) I convert the B parameter from micro-meter to m² : B = B / 1000000
2) I convert my wavelenght from nm to micro-meter : wv = 500 / 1000

But the result I got seems incorrect, I got no dispersion !!!
Maybe there is a problem with my units ?