Central versus peripheral thickness in the human cornea explained

The human cornea is thicker in the periphery than the center and it has been suggested that this must be due to greater numbers of lamellae in the peripheral corneal stroma. The purpose of this study was to use high-resolution ultrastructural imaging to determine if the greater thickness of the peripheral cornea is due to the presence of more lamellae or if there is some other anatomical explanation.

In this study, full thickness corneas from three human donors were processed for light microscopy (LM) and transmission electron microscopy (TEM). Images were taken in three distinct stromal regions (anterior, middle, and posterior) from the central and peripheral cornea. Stromal thickness was evaluated by LM while TEM was used to evaluate numbers and thicknesses of lamellae, mean collagen fibril diameter, and mean collagen fibril density.

Mean stromal thickness was significantly thinner in the central (415 ± 34 µm) compared to the peripheral (536 ± 29 µm) cornea (P = 0.009). Numbers of lamellae were not significantly different between central (246 ± 14) and peripheral (251 ± 14) cornea. Average lamellar thickness was not different across all regions of the cornea, except for the peripheral posterior where the lamellae were approximately 50 % thicker (P < 0.05). Collagen fibril diameters were larger in the peripheral cornea by approximately 30 % when compared to the central cornea, in all regions (P < 0.01).

This study shows that it is an increase peripheral posterior lamellar thickness, rather than an increase in the number of lamellae, that accounts for the increase in corneal stromal thickness in the periphery of the human cornea. While collagen fibril diameters are greater throughout the peripheral stroma, the lamellae in the mid and anterior peripheral stroma are not thicker than centrally.