Morphometric characteristics of central retinal artery and vein endothelium in the normal human optic nerve head

This study documents the morphometric features of arterial and venous endothelia in the different laminar regions of the normal human optic nerve head and speculates on the hemodynamic characteristics of the central retinal artery (CRA) and central retinal vein (CRV).

Twenty normal human eyes were used. Microcannulation techniques were used to label the cytoskeleton and nuclei of endothelial cells in the CRA and CRV, after which images were captured using confocal microscopy. Length, width, length-to-width ratio, and area measurements were obtained from endothelium and its nuclei. Nucleus position with respect to cell apex and direction of blood flow was also quantified. Comparisons were made between prelaminar, anterior lamina cribrosa, posterior lamina cribrosa, and retrolaminar regions. Venous and arterial endothelial cell morphology was also compared.

There was significant variation in venous endothelial morphology across the different laminar regions; however, no differences were found in arterial endothelial characteristics (all P > 0.1065). Significant differences were found between arterial and venous endothelium in all laminar regions apart from the posterior lamina cribrosa, where only nuclear area (P = 0.0001) and nucleus position (P = 0.0088) were found to be different.

Arterial-like appearance of venous endothelium in the posterior lamina cribrosa, where pressure gradient forces are predicted to be greatest and CRV luminal diameter is known to be narrowest, implicates this as a site of altered hemodynamic stress. Heterogeneity of venous endothelium may have relevance for understanding ocular vascular diseases such as central retinal vein occlusion.