Hypothetical proposal for the course of retinal blood vessels in the posterior pole—description and its clinical implications

Abstract

Background: Branch retinal vein occlusion (BRVO) is the second-most common retinal vascular disorder. Arteriosclerotic changes at the site of obstruction and hemodynamic turbulence within the vessels are considered risk factors. Overcrossing of the vein by an artery has traditionally been considered to increase the risk of BRVO. Recent studies using optical coherence tomography and optical coherence tomography angiography have suggested a higher prevalence of vein-over-artery crossings in this disease. Nevertheless, uncertainty persists as to why some patients, even those with the same disease duration, have varying degrees of venous dilation and develop sufficient collaterals, while others develop substantial ischemia and its sequelae. Hypothesis: Herein, it is hypothesized that because retinal blood vessels are transparent, tubular, and collapsible conduits coursing over a hollow spherical surface, the changes related to AV crossings over the entire course of a vessel, rather than at any single isolated crossing, could contribute to the risk, natural progression, and outcomes of BRVO. The study analyzed color fundus photographs from two image datasets. The first dataset comprised 100 randomly selected images from the author’s own collection at the Rajendra Prasad Center for Ophthalmic Sciences. The second dataset comprised 100 images from the MESSIDOR database; three images were excluded owing to poor focus. Using 394 observations from 197 retinal photographs, four distinct patterns of AV crossing along the course of blood vessels were recognized: (A and B) wicker basket, (C) straight, (D) widely spaced, and (E) indeterminate. The percentages of tight wicker, loose wicker, straight, widely spaced, and indeterminate patterns in the two image sets were 19% (38/200) and 16.5% (32/194), 22.5% (45/200) and 27.8% (54/194), 16.5% (33/200) and 15.5% (30/194), 22.5% (45/200) and 28.4% (55/194), and 19.5% (39/200) and 11.9% (23/194), respectively. Hence, the wicker basket pattern was the most common AV crossing pattern in both image sets. Conclusions: The wicker basket pattern may provide structural stability and aid in maintaining pressure gradients within the retinal vascular bed. This observation of variable AV relationships at consecutive crossings may improve our understanding of the pathogenesis, natural history, and outcomes of BRVO. Future longitudinal studies including patients at risk of BRVO, or retrospective analyses of patients with BRVO who had ophthalmic examinations and archived fundus images before the vascular event, should verify the relevance of these observed vascular patterns.