RETINAL DEVELOPMENT AND ITS STRUCTURES
The human eye begins to develop at embryonic day (E) 18. The visual groove is formed at E22 before continuing to sag to form the visual vesicle, which expands to form the inner and outer layers of the optic cup. The RPE layer begins to differentiate around E30, with pigment particles found in RPE cells at E35. A set of genes (including PAX6, LHX2, RAX, and SIX3) expressed in the neural plate before E8 are involved in eye determination and eventually form the optic cup (Hoon et al., 2014). In general, vertebrate RPE cells develop and differentiate from optic vesicles. During embryonic development, early optic vesicle cells have bidirectional potential and can develop into the retinal neocortical layer or the RPE layer. The cell fate decision and differentiation of RPE precursor cells is not spontaneous but rather influenced by a variety of microenvironmental factors. Under the influence of extracellular signals, differentiation is guided in strict temporal and spatial order.