At the eye doctors, why do brown eyes take two eyedrops to dialate the pupils?

Question

Well, I was at the eyedocters, And I overheard the doctor in the next room say "Because she has brown eyes, we are going to need to do two drops in each eye to make the pupils dialate" Why only for brown eyes?

Answer 1

Because brown eyes are darker, it's harder to see inside them.  The same two drops would be needed for someone with black eyes or really dark hazely types.

Answer 2

darker pigmented eyes do not take to the drops like lighter eyes do.