Distributions of elements in the human retinal pigment epithelium
R. J. Ulshafer, C. B. Allen and M. L. Rubin
Department of Ophthalmology, College of Medicine, University of Florida, Gainesville 32610.
Distributions of elements above the atomic number of sodium were mapped in
the retinal pigment epithelia of eight human eyes. X-ray energy spectra and
maps were collected from cryofixed, freeze-dried, and epoxy-embedded
tissues using energy-dispersive x-ray microanalysis. All eyes had high
concentrations of phosphorus in the nuclei of retinal pigment epithelial
cells. Melanosomes were rich in sulfur, zinc, calcium, and iron. Lipofuscin
and cytoplasm contained only phosphorus and sulfur in detectable amounts.
Drusen, when present, contained phosphorus and calcium. Six eyes had a
prominent aluminum peak recorded from melanosomes, nuclei, and Bruch's
membrane. In one pair of 90-year-old eyes, small, electron-dense deposits
surrounded many melanosomes and contained mercury and selenium. Retinal
pigment epithelial melanosomes may bind and accumulate metals and other
potentially toxic ions over time, preventing them from reaching the neural
retina.
