The iris regulates the amount of light entering the eye and is not renewable.
The iris is rich in pigment and is a disc of hollow membrane-like tissue. The “black eye” seen from the outside is the color of the iris pigment.
The hollow structure in the center of the iris is the pupil. When the outside light is strong, the pupil narrows, i.e., the iris dilates, reducing the amount of light entering the eye and protecting the fundus of the eye from being damaged by too much light. When the light is weak, the pupil enlarges, i.e. the iris tenses, increasing the amount of light entering the eye and allowing the eye to see more clearly.
The iris may be damaged or even detached from the inner eye during trauma or inner eye surgery, such as cataract surgery. You should try to return the iris back into the eye during the surgery to avoid photophobia and blurred vision in dark light after surgery.