Cells resembling intraventricular macrophages are present in the subretinal space of human foetal eyes

The subretinal spaces (SRS) in 17 human foetal eyes were investigated by light microscopy and scanning and transmission electron microscopy. A hitherto undocumented group of pleomorphic cells was detected on the apical surface of the retinal pigment epithelium (RPE) and on the undersurface of the neural retina. These cells formed a regularly spaced array in the peripheral SRS, particularly in the most anterior portion nearest the ciliary body anlage. The morphology of the SRS cells ranged from a small round or ovoid form with a few short basal pseudopodia to an extremely flattened dendritic form. Ultrastructural features, such as large melanophagolysosomes, consistent with a phagocytic function, were observed in some cells. These SRS cells bore remarkable resemblance to epiplexus and supraependymal cells, considered to be the resident population of macrophages on the ventricular surfaces of the brain. This morphological parallelism, together with the anatomically homologous location, is strong evidence that SRS cells represent a normal population of macrophages in the developing human eye. No features consistent with an RPE or neuronal origin were observed. The possible role of these cells as transient phagocytes in the SRS with a possible destiny as retinal microglia is discussed.