Author Response: Morphometric Characteristics of Central Retinal Artery and Vein in the Optic Nerve Head of Patients with Diabetes

We appreciate the interest that Dr. Dimitrova has expressed in our paper, ¹ published in the March 2011 issue. ² We agree that a detailed morphometric analysis of the central retinal artery and vein inside the optic nerve head has not been undertaken in patients with diabetes. Diabetic retinopathy remains a leading cause of blindness in the working population of developed countries. However, a general view of the pathogenesis of diabetic retinopathy is that it is a disease of multifactorial origin, with a range of microvascular and neuroglial abnormalities. We are still unable to provide sufficient solid evidence to determine the cause-and-consequence relationship and interpret how the pathologies found in experimental and clinical studies relate to one another and how they contribute to disease progression. ^3,4  

There is abundant evidence suggesting early changes in retinal perfusion before the onset of diabetic retinopathy that may be related to inflammatory changes, loss of capillaries, and progressive ischemia and hypoxia. Structural and functional changes in the retinal vasculature are closely related to diabetes and diabetic retinopathy. The pathogenic role of the vascular endothelium in diabetic retinopathy is thought to be critical, as it is a vast and heterogeneous organ faced with diverse challenges. In addition to regulating vascular tone, the endothelial cells carefully balance and dynamically regulate both barrier function and selective permeability to solutes and immune cells. Endothelial cells in specific locations such as the lamina cribrosa may meet different mechanical forces, including fluid shear, hydrostatic pressure, and cyclical stretching. In pathologic conditions such as diabetes, both hemodynamic conditions and endothelial cells could be significantly altered. In previous studies, our group has attempted to quantify the morphologic, ⁵ pharmacologic, ⁶ and functional ⁷ changes in the ocular vasculature in the early stage in rat models of induced diabetes. We have also examined pharmaceutical interventions for ameliorating the vascular changes in induced diabetes. ⁸  

There is no doubt that morphologic analysis of endothelial cells from human eyes could provide valuable information toward understanding the possible pathogenic role of endothelial cells in many ocular diseases. Fortunately, the intravascular perfusion fixation and staining technique developed in our laboratory allows us to investigate the intracellular changes in the whole retinal and choroidal microvasculature and their relationship with retinal neurons and glia in normal, aging, and diseased human donor eyes. ⁹ We hope to gain new information from human donor eyes that will help us to further bridge the gap between the findings in experimental and clinical studies. 

We cannot overemphasize the importance of study of the pathogenesis of diabetic retinopathy, particularly the possible pathogenic roles of the retinal vasculature. Although the roles of the central retinal artery and vein in the pathogenesis of diabetic retinopathy remain unclear and the role of endothelial cell dysfunction is not well understood, in the future, as we continue to expand our collection of human donor eyes, we may well be in a position to contribute to the understanding of endothelial cell changes in diabetic human eyes and to complement the clinical study by Dimitrova et al. ¹⁰