Purpose: To describe a model predicting endothelial cell (EC) loss after iris-fixated phakic intraocular lens (pIOL) implantation, taking distance from the edge of the pIOL to endothelium into account. Methods: This prospective observational study, monitored long term EC changes in 306 eyes after pIOL implantation. EC density (ECD) was determined preoperatively, 6 months postoperatively and then yearly, up to 8 years postoperatively. Mean follow-up was 31.7 +/- 25.7 months. All eyes underwent anterior segment optical coherence tomography to determine minimum distance from the edge of the pIOL to endothelium. Linear mixed model analysis was performed to present a model which describes EC loss as a linear decrease and an additional decrease depending on the postoperative edge-distance of the patient. Results: Mean minimum edge-distance was 1.43 +/- 0.23mm (range 0.70-2.21mm). For this mean edge-distance, the model predicted a yearly EC loss of 1.0%, whereas an edge-distance of 1.20mm resulted in a yearly EC loss of 1.7%, and 1.66mm led to a yearly EC loss of only 0.2%. Furthermore, the model predicted that for patients with preoperative ECDs of 3000, 2500 or 2000 cells/mm2 and edge-distances of 1.43mm, a critical ECD of 1500 cells/mm2 (at which point pIOL explantation and cataract extraction can still safely be performed) will be reached at 56, 37, and 18 years after implantation. Conclusions: The presented model predicts EC loss after iris-fixated pIOL implantation in relation to the measured edge-distance, patient age, and preoperative ECD, which can assist ophthalmologists in patient selection and follow-up process of pIOLs.