Although primary retinal tumors were recognized clinically for many years, their pathologic nature was long uncertain. They were classified as to their stage of growth: early as fungus medullaris, and late as fungus haematodes. Von Graefe1 was doubtful as to their essential nature and believed them to be hyperplasias of the retina, carcinomas or sarcomas. It was not until 1864 that Virchow first considered these primary retinal tumors as gliomas arising from preexisting glia cells of the retina and analogous to gliomas of the brain. However, he also described their malignant transformation into gliosarcomas. In 1868, Hirschberg and Knapp independently defined the histologic picture of the primary tumors and their metastatic growths as being purely gliomatous and never sarcomatous.
All the primary epithelial tumors of the retina were called gliomas, in spite of the fact that they obviously did not have a homogeneous histologic structure, until Flexner2 separated
ROY R. GRINKER. GLIOMAS OF THE RETINAINCLUDING THE RESULTS OF STUDIES WITH SILVER IMPREGNATIONS. Arch Ophthalmol. 1931;5(6):920–935. doi:10.1001/archopht.1931.00820060088009