Since the introduction of the first coralline hydroxyapatite porous orbital implant as eye replacement in the early 1980s, numerous other modified porous implants have been developed. Due to the different design of the existing studies concerning long-term safety with, in some cases, relatively short follow-up, a comparison is difficult and none of the implant types can be clearly identified as being superior. Factors affecting the exposure rate of the implant seem to be the implant coating, the surgical technique and the condition of the patient's tissue at the beginning of surgery.