March 2012
Volume 53, Issue 3
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Letters to the Editor  |   March 2012
Morphometric Characteristics of Central Retinal Artery and Vein in the Optic Nerve Head of Patients with Diabetes
Author Affiliations & Notes
  • Galina Dimitrova
    Neuromedica Polyclinic, Skopje, Macedonia.
Investigative Ophthalmology & Visual Science March 2012, Vol.53, 1637. doi:10.1167/iovs.12-9572
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      Galina Dimitrova; Morphometric Characteristics of Central Retinal Artery and Vein in the Optic Nerve Head of Patients with Diabetes. Invest. Ophthalmol. Vis. Sci. 2012;53(3):1637. doi: 10.1167/iovs.12-9572.

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I read with great interest the excellent study by Kang et al. 1 in the March 2011 issue. In the context of their study, this short communication is intended to address an aspect of the ocular pathology in diabetic retinopathy. 
Diabetic retinopathy is among the leading causes of blindness in the working population in developed countries. 2 However, the exact etiology and the mechanism of disease progression of diabetic retinopathy are still unresolved. Disturbances have been detected in many aspects of ocular circulation in diabetes, but the role of the hemodynamics in diabetic retinopathy has not been clearly defined. 
In a prospective follow-up study of patients with diabetes, the initial changes in the retrobulbar circulation during progression of diabetic retinopathy occurred in the central retinal vein. 3 The alteration of the blood flow in the central retinal vein consisted of increased maximum and minimum blood flow velocity and increased index of resistivity. Because the blood flow velocity in the central retinal artery did not change in accordance with the changes in the central retinal vein, a local circulatory disturbance in the central retinal vein of patients with progression of diabetic retinopathy was suggested. 
The central retinal artery and vein are in close relationship inside the optic nerve, especially at the level of the lamina cribrosa, where the artery retains its round shape, whereas the vein, being pressed by the artery, takes on an oval or crescent shape. 4 The gradual constriction of the central retinal vein at this level acts as a throttle that maintains the intraretinal capillary and venous pressure. Even a relatively small reduction in radius greatly increases the difference in the blood pressure on either side of the lamina cribrosa and results in altered blood flow in the vessels inside the optic nerve head. Therefore, variations in vascular caliber may be expected in the central retinal artery and vein in the optic nerve head in diabetes, which may be a cause for the alteration of the retrobulbar venous circulation that was detected in the above-mentioned study. 3 The morphometric characteristics of the blood vessel endothelium are influenced by the blood flow pattern. 5 In their study, Kang et al. 1 reported that, in the central retinal vein, they detected an arterial-like appearance of the venous endothelium in the posterior lamina cribrosa, where pressure gradient forces are predicted to be greatest, and the luminal diameter of the central retinal vein is known to be narrowest. They suggested that changes in venous endothelial morphology between the posterior lamina cribrosa and retrolaminar regions most likely reflect local hemodynamic force alteration that may predispose to venous endothelial injury at this site, particularly during pathologic states in which shear stress and tissue pressures are modified. As a consequence, this region of the optic nerve head may be a site of thrombus formation and may be important in the etiology of diseases such as central retinal vein occlusion. 
To my knowledge, a detailed morphometric analysis of the central retinal artery and vein inside the optic nerve head has not been undertaken in patients with diabetes. The results of such an investigation may indicate an alteration in blood vessel diameter in the major blood vessels inside the optic nerve. Furthermore, an analysis of the morphometric characteristics of the endothelium of the central retinal artery and vein in diabetic patients suggests the pattern of blood flow in these blood vessels. Since the total retinal blood inflow and outflow occur via the central retinal artery and vein, the results are invaluable for understanding the overall intraretinal microcirculation in patients with diabetes. 
References
Kang MH Balaratnasingam C Yu PK . Morphometric characteristics of central retinal artery and vein endothelium in the normal human optic nerve head. Invest Ophthalmol Vis Sci. 2011;52:1359–1367. [CrossRef] [PubMed]
Resnikoff S Pascolini D Etya'ale D . Global data on visual impairment in the year 2002. Bull World Health Org. 2004;82: 844–851. [PubMed]
Dimitrova G Kato S Yamashita H . Relation between retrobulbar circulation and progression of diabetic retinopathy. Br J Ophthalmol. 2003;87:622–625. [CrossRef] [PubMed]
Taylor AW Sehu W Williamson TH . Morphometric assessment of the central retinal artery and vein in the optic nerve head. Can J Ophthalmol. 1993;28:320–324. [PubMed]
Fisher AB Chien S Barakat AI . Endothelial cellular response to altered shear stress. Am J Physiol Lung Cell Mol Physiol. 2001;281(3):29–33.
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