Uncontrolled Oxygen Levels in Cultures of Retinal Pigment Epithelium: Have We Missed the Obvious?

Retinal pigment epithelium (RPE) is the outermost layer of retina located between the photoreceptor cells and the choroid. This highly-polarized monolayer provides critical support for the functioning of the other parts of the retina, especially photoreceptors. Methods of culturing RPE have been under development since its establishment in 1920s. Despite considering various factors, oxygen (O 2 ) levels in RPE microenvironments during culture preparation and experimental procedure have been overlooked. O 2 is a crucial parameter in the cultures, and therefore, maintaining RPE cells at O 2 levels different from their native environment (70-90 mm Hg of O 2 ) could have unintended consequences. Owing to the importance of the topic, lack of sufficient discussion in the literature and to encourage future research, this paper will focus on uncontrolled O 2 levels in cultures of RPE cells.