What's this black circle around my iris?

[sarmatian]

I have light brown eyes, but around my iris (so the brown part) I have this black circle.
My dad has it, but my mom doesn't. What's it called?

 

[greycelzoomer]

OP wants us to use our imagination

 

[Mosh12]

Variation in eyes

 

[Suimaxxer]

U have 1 week left to live

 

[hattrick]

Limbal ring

 

[sarmatian]

Limbal ring

That's it, thanks.