Clinical manifestations of functional disturbances of the retinal pigment epithelium

The retinal pigment epithelium (RPE) serves a variety of different functions and impairment of these functions can lead to a multitude of different diseases of the posterior segment of the eye. The RPE plays an important role as an ion and fluid pump for the reabsorption of subretinal fluid in retinal detachment. On the other hand, defects in this pump function and in the outer blood-retinal barrier formed by the RPE, lead to fluid retention in inflammatory diseases. Metaplasia of RPE cells to myofibroblasts can lead to proliferative vitreoretinopathy and tractive retinal detachment. Early age-related maculopathy is caused by disturbances of phagocytosis and metabolism of the RPE. Imbalance of the physiological equilibrium between vasoproliferative and vasoinhibitory factors secreted by the RPE is probably involved in the development of atrophic or neovascular forms of advanced age-related macular degeneration. Mutations in the different steps involved in regeneration of the visual pigment (visual cycle) may lead to retinal dystrophy. Finally, immunoregulatory properties of the RPE are responsible for the phenomenon of immunological privilege, which may facilitate clinical interventions such as gene therapy and RPE transplantation.