Chloride concentrations in the corneal epithelium and stroma from different species

Electrolytes in the cornea: a therapeutic challenge

BACKGROUND

Reported here are the results of electrolyte measurements in different layers of 70 apparently normal human corneas.

METHODS

Samples were examined by energy-dispersive X-ray analysis under calibrated conditions in a scanning electron microscope. The method allows the simultaneous quantitative analysis of, among others, sodium (Na), chloride (Cl), phosphorus (P) and potassium (K). The results are related to the dry weight of the analyzed samples. Four distinct layers, subepithelium, middle stroma, posterior stroma and Descemet's membrane, were analysed in each cornea.

RESULTS

In the middle stroma we found concentrations of: sodium 0.609 +/- 0.13, chloride 0.557 +/- 0.115, potassium 0.058 +/- 0.02 and phosphorus 0.038 +/- 0.01 (mol/kg dry weight) [corrected].

CONCLUSION

The collation of normal electrolyte concentrations provides reference values for future studies on changes of the corneal electrolyte composition in diseased or injured eyes. The electrolyte composition of rinsing fluids or eye drops should be adjusted to that of the corneal stroma. Phosphate buffer, for example, is not a good vehicle for topical eye treatments and should be replaced by organic buffering systems.

Anatomy and morphology of the cornea of bovine eyes from a slaughterhouse

Over a 1-year period, isolated bovine eyes were obtained from a slaughterhouse and assessed within 3 h post mortem. The gross disposition (including damage or disease) and corneal surface characteristics (overall appearance and wettability) were assessed by visual inspection and light and scanning electron microscopy. The results from 315 eyes (assessed to be free of gross abnormalities or damage) showed that the corneal thickness was 1015 ± 104 μm (mean ± SD; n = 315). Measures on 100 of these eyes revealed corneal dimensions averaging 29.8 ± 1.3 mm horizontally and 23.9 ± 1.5 mm vertically. The horizontal corneal diameter was greater in eyes with thicker corneas (r = 0.917). Regardless of thickness, corneas evaluated within 3 h post mortem had a uniform thickness within ± 3% from center to edge. Histology and scanning electron microscopy revealed that even corneas subjectively assessed to be in good condition had relatively large numbers of exfoliating cells at the epithelial surface, indicating that the corneal surface of bovine eyes from the slaughterhouse is likely to be slightly compromised. Scanning electron microscopy showed the endothelium to be a mosaic of uniformly sized polygons of which 67.1 ± 2.7% were six-sided cells (hexagons).