The retinal pigment epithelium (RPE) occupies an interesting anatomical location, situated between a high-flow network of blood vessels (the choroid) and the most metabolically active cells in the body (the photoreceptors). Its position alone would suggest that the RPE has an important role in both normal physiologic processes and disease.
Yet our understanding of this tissue remains limited. Age-related macular degeneration serves as a case in point. Of the 4 leading causes of blindness in the developed world (the others being cataract, glaucoma, and diabetic retinopathy), age-related macular degeneration is the only one that has failed to yield in a considerable way to our efforts at therapy. That the RPE plays a role in age-related macular degeneration is suggested by extensive pigmentary disturbance, which typically occurs well in advance of any known photoreceptor changes. The only therapy of proven benefit is photocoagulation for choroidal neovascularization, which, sadly, is only helpful in a small fraction of patients. Recently, there has been a satisfying increase in the number of clinical studies, but although some may eventually prove efficacious, reports of longer-term outcomes do not seem to support all of the initial enthusiastic claims. Rather, it seems that more effort, expense, and morbidity is resulting in ever-smaller percentages of patients who benefit.
The Retinal Pigment Epithelium. Arch Ophthalmol. 2000;118(5):737. doi: