Why do brown eyes not dilate as readily/big as lighter coloured irises, such as blue eyes?

Question

Including on drugs that dilate the pupils (such as mydriatics, etc.), brown/dark brown eyes do not dilate to nearly the same extent/as easily as lighter coloured eyes. Why is this?

In:

Answer 1

Comment
byu/LesserOmentum from discussion
inaskscience

Answer 2

I can‘t really think of a reason that fits generally, but I have an idea. Like on what color your hair or skin has, the color of your eyes is determined by the interaction of many genes. It‘s possible that some of these genes also interact with the muscles that control the dilation on drug influence, but this won‘t fit generally. As an example: people with active gene 1, 2, 3 have brown eyes and people with active gene 4, 5, 6 have brown eyes, but only gene 3 interacts with our needed muscles, so person 1 will show your observation but person 2 won‘t, although both have brown eyes.