This ridge is called a protruding iris collarette, a rare condition that might be hereditary but is definitely strange looking! Here's more on this odd condition:
The iris collarette marks the thickest region of the iris, and it separates the inner pupillary portion of the eye from the outer ciliary portion. It’s also the part of the eye where the sphincter muscle (no, not that sphincter muscle), and the dilator muscle overlap. Iris collarettes are typically flat, but as seen in this patient, they can sometimes extrude outwards in a distinctive ring-like pattern.Surprisingly, the woman's symptoms were caused by an allergic reaction, and the protruding iris collarette was nothing more than an "incidental finding".