The flexible iris prosthesis according to Koch with a customized iris design serves for anterior segment reconstruction in patients with partial or complete aniridia. It is designed for implantation in the ciliary sulcus and is recommended only for pseudophakic or aphakic eyes. The multilayered implant consists of a core of a silicone matrix with incorporated color pigment coated with another layer of medical grade silicone. As a design variant the implant is available with or without an additionally embedded tissue layer. Without tissue the implant is more flexible, can be easily folded and perfectly adapts to the anatomical course of the sulcus. In contrast, implants with tissue show a greater rigidity and provide a better grip for sutures. This article describes various techniques for implantation of partial and full prostheses and gives instructions for calculating the implant size. Full prostheses can be combined with other reconstructive measures, such as sutured intraocular lenses and are particularly helpful in silicone oil surgery by avoiding endothelial contact. With careful consideration of the indications and application the flexible iris prosthesis is a valuable extension of the spectrum of reconstructive anterior segment surgery.