Xanthelasma from both upper eyelids of a patient were examined by electron microscopy. The cytoplasm of the foam cells was filled with lipid droplets that were not bounded by a membrane. The lipid itself dissolved out during tissue preparation despite osmium or glutaraldehyde-osmium fixation, indicating that the lipid is highly unsaturated.
Anderson DR. Ultrastructure of Xanthelasma. Arch Ophthalmol. 1969;81(5):692-694. doi:10.1001/archopht.1969.00990010694015