How common is heterochromia in black people?

ive tried googling this but nothing comes up im a black female of twenty years of age and im exteremly curious of how I have heterochromia when I would thin I have more than enough melanin .. please someone answer
this

I'm from Côte d'Ivoire and I have central heterochromia in my eyes. They are light green in the center and hazel on the outside. People ask me all the time where I bought my colored contacts, and I have to say that they aren't contacts over and over. I have acquired sectoral hypochromia in my right eye, and so does my maternal grandmother, but we don't know anyone else with it. I've never seen any statistics about how prevalent it is among blacks.

Quote from the web site below:

"There is no race or sex predilection. It affects both genders equally and is typically manifested in young to middle adulthood. "

http://eyewiki.aao.org/Fuchs_Heterochromic_Iridocyclitis_and_Secondary_Glaucoma