Differentiation of stem cells to human retinal organoids. (A) Stem cells colonies are cultured (iPSCs or ESCs). (B) Day 3 of differentiation. Aggregation of stem cells is almost complete. (C) Day 7 of differentiation. Neuronal vesicles, indicated with a white arrowhead, begin to differentiate. (D) Day 200 of differentiation. The lighter outer edge of the organoid, indicated by the white arrow, is retinal tissue. Photoreceptors are present on the outer edge of the organoid. RPE is also present, marked by a white asterisk.