
Degenerative diseases of the retina such as age-related macular degeneration or retinitis pigmentosa are the most common causes for loss of vision [1]. Existing in vitro or in vivo model systems for the testing of new pharmaceutical compounds as well as for mechanistic research recapitulate the structure and complexity of the human retina only to a very limited extent. New achievements in the field of stem cell biology, in particular the induced pluripotent stem cells (iPSC), enable the generation of complex 3D tissue structures: Stem cell-based retinal organoids (RO) feature multiple layers of a variety of different cell types representing parts of the structure of retinal tissue [2]. However, even ROs are still limited, especially with regard to the interaction of the photoreceptors with the surrounding tissue, their maturation and the vascularization.