During a study of lipids in the pigment epithelium of the normal human retina, it was observed that there were a large number of round granules, basally located in the cells, which stained with Sudan black B even in paraffin sections. These granules were colored weakly or not at all by the red Sudans and were not visible in sections stained by routine histological methods. The intermingling of sudanophilic granules with the melanin granules gave an initial impression that some of the melanin must be sudanophilic. Examination of unstained sections showed, however, that the majority of the sudanophilic granules were pale, almost colorless forms.
This finding was unexpected, since it is generally thought that without special techniques sudanophilic substances are seen in the human pigment epithelium only during disease. It has long been known that the pigment epithelial cells of many lower vertebrates contain lipid inclusions, distinguishable from mitochondria and
STREETEN BW. The Sudanophilic Granules of the Human Retinal Pigment Epithelium. Arch Ophthalmol. 1961;66(3):391-398. doi:10.1001/archopht.1961.00960010393017