Mapping the Time Line of Development in Each Layer of Human Foetal Retina

Introduction: There is need to elucidate the histological developmental stages of various layers of retina, to understand the process better and provide clinically significant insights. Aim: To study the details and chronology of in utero development of different layers of retina. Materials and Methods: To study time of appearance, differentiation and organization of all layers of central retina in different gestational age groups. Retina was studied histologically in 27 foetuses from18th to 34th weeks of gestation. Results: We found the period of mid gestation (19th - 21st week of gestation) to be the defining time for retinal layers: The bruch's membrane was fully formed at 20th week of gestation; the photoreceptor layer became well defined at 21st week of gestation; both the nuclear layers and both the plexiform layers and the ganglion cell layer became distinct at 19th week of gestation. Before the 19th week, outer and inner neuroblastic zones separated by the neuropil were seen. Well defined nerve fibre layer and inner limiting membrane was present at 18th week. The outer limiting membrane was first appreciated at 32nd week of gestation. Foetal retinal pigment epithelium was cuboidal and filled with melanin granules while no trace of lipofuscin pigment was found under fluorescent microscope. Conclusion: Detailed data on retinal histogenesis and its timeline might aid in directed differentiation of retinal cell types from stem cells for therapeutic purposes.