THE CORNEAL STROMA - AN INHOMOGENEOUS STRUCTURE

Purpose: This study was conducted to determine the elemental compositi on of the human cornea. Special attention was paid to corneal stroma i nhomogeneity. Methods: Seventy human corneas were examined by means of energy-dispersive X-ray analysis. Epithelium, subepithelium, middle s troma, sub-Descemet layer, Descemet's membrane and endothelium were su bjected to repeated measurements. Results: In the cellular layers the phosphorus concentrations were high [0.35 mol/kg dry weight (dw) in th e epithelium and 0.403 mol/kg dw in the endothelium]. Similar concentr ations were found for sulphur (0.38 mol/kg dw in the epithelium). Stro mal layers showed high contents of sulphur: 0.26 mol/kg dw. The phosph orus concentration was found to be higher in the subepithelium than in the middle stroma. Sulphur concentrations were highest in Descement's membrane, followed by the subepithelium and the middle stroma. Discus sion: Nucleic acids and energy-containing phosphates explain the high levels of phosphorus in the cellular layers. The high sulphur concentr ations may be related to the phosphoadenosinphosphosulfate and protein turnover in the epithelium. We interpret the inhomogeneous distributi on of phosphorus in the stroma as a function of the density of keratoc ytes. An evalulation of all known sulphur-containing biochemical compo nents of the stroma (0.217 mol sulphur/kg dw) corresponds to our measu rements. In contrast to former results we find the corneal stroma to b e an inhomogeneous structure.