As Dr. Hagan suggests, first see an ophthalmologist to make sure everything in the eye department is healthy.
If that turns out to be the case, then you might want to look into a condition called "periorbital hyperpigmentation." A dermatologist can give you the word on this, and there is plenty of information to be had with a google search, too.
Apply cucumber slice over your eyes for 15 minutes as well as lemon juice, aloe vera. It will helps to remove your dark circles.
1. Many comments on this before use search feature and archives to read.
2. Have an Eye MD ophthalmologist do an eye exam to be sure they are okay.
3. If eyes okay then use cover creams to lighten. Discussed previously see #1 above
JCH MD