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J Khan, T Day, RS Clemett; Anatomy of Retinal Arteriovenous Crossings in Hypertensive Subjects . Invest. Ophthalmol. Vis. Sci. 2002;43(13):2613.
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Purpose: Branch retinal vein occlusion (BRVO) is a common retinal vascular problem seen in ophthalmic practice and is associated with hypertension in 50-75% of cases(1). Histopathological studies of arteriovenous(AV) crossing sites are scarce, particularly in hypertensives. The aim of this study was to elucidate whether the anatomical features, which predispose to artery over vein crossings being the preferential site for BRVO are exaggerated in hypertensive patients; hence offering an explanation for the increased risk of such an event occurring in these patients. Method: Ten pairs of donor eyes obtained for corneal graft donation were used in the study. Subjects were defined as hypertensive if they had a history of treatment and follow-up for hypertension. After removal of the donor corneal button, globes were fixed in buffered glutaraldehyde. AV crossings were excised from retinae and processed for transmission electron microscopy (TEM). Serial 1-micrometer sections were taken for light microscopy. 70nm sections were taken before, at and after AV crossings for TEM. Alterations in vein cross-sectional area, deviation and focal adventitial thickening were examined. Result: Veins were seen to change direction abruptly at the site of AV crossings. Focal adventitial thickening of the extracellular matrix and adventitia opposite the point of AV contact was noted to be more pronounced in this series of hypertensives than with a previous series of normotensives(2). Most notable was the vein lumen increase in size in the hypertensive subjects at the crossing. This is contrary to the widely held belief that the vein is constricted at this point. We also noted areas of irregularity and attenuation of the vein wall at the point of contact with the artery, which may represent areas of weakness, subject to leakage and subsequent thrombus formation. The endothelium in the hypertensive subjects showed degenerative features not found in the age-matched controls of the preceding study mentioned above. Conclusion: Alterations to vein morphology at AV crossing sites are exaggerated in hypertensive subjects, and we observed evidence of weakening of the vessel wall at the point of contact. Our results suggest surgical intervention techniques may be inappropriate for BRVO. Ref: 1. Orth DH, Patz A. Retinal branch vein occlusion. Surv.Ophth. 1978;22:357-76. 2. Jefferies P, Clemett R, Day T. An anatomical study of retinal arteriovenous crossings and their role in the pathogenesis of retinal branch vein occlusions. Aust.N.Z.J.Ophthalmol. 1993;21:213-7.
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