DOES THE HUMAN CORNEA CONTAIN SILICON

Background: Our study investigated the presence, type and quantity of silicon in the human cornea. We report the results of silicon measurem ents in the corneas of silicotic individuals, bricklayers and apparent ly normal human individuals and offer a hypothesis for the mechanism o f silicon deposition in the human cornea. Methods: We examined corneas from 13 deceased subjects who suffered from silicosis, 2 bricklayers and 6 apparently healthy subjects. Cornea samples were examined by ene rgy-dispersive x-ray analysis (EDXA) under calibrated conditions in a scanning electron microscope (SEM). The EDXA detector was a silicon-fr ee germanium crystal. Five distinct layers (epithelium, Bowman's membr ane, central stroma, Descemet's membrane and endothelium) were analyze d in each cornea. The method allows simultaneous semiquantitative anal ysis of, among other elements, silicon, calcium and oxygen. We measure d amorphous silicon and visible particles of silicon. Results: We foun d amorphous silicon in low concentrations in 38% of the silicotic corn eas and in very low concentrations in 29% of the healthy corneas. Bric klayers showed high concentrations of amorphous silicon. These accumul ations of silicon were predominantly located in Descemet's membrane. S ilicotic corneas showed significantly more silicon-containing particle s than corneas of healthy controls (chi(2)-test, P< 0.01). Conclusion: Normal corneas contain very low amounts of silicon. Longterm exposure to inhalative silicon dusts results in only very slightly increased l evels of amorphous silicon in the cornea. However, silicon-containing particles accumulate in the cornea of silicotic individuals. Bricklaye rs incorporate more amorphous silicon into the cornea.