Venous Nicking Without Arteriovenous Contact: The Role of the Arteriolar Microenvironment in Arteriovenous Nickings.

IMPORTANCE: Arteriovenous nickings (AVNs) in the retina are the cause of retinal vein occlusions and are also surrogates of cerebrovascular aging. The prevalent mechanistic model of AVNs stating that arteries crush veins remains somewhat unchallenged despite the lack of evidence other than fundus photographs. Here, we observed that venous nicking may be observed in the absence of physical contact with an arteriole. OBSERVATIONS: This observational study, conducted from January 2013 to September 2014, included 7 patients showing remodeling of a venous segment close to a retinal arteriole without arteriovenous overlap were imaged by adaptive optics imaging. Affected venous segments showed a variable association of nicking, narrowing, deviation, and opacification. Venous segments were deviated toward the arterioles in 6 of the 7 cases. The degree of venous narrowing ranged from 40% to 77%, while at these sites, the width of the intervascular space ranged from 16 µm to 42 µm. Similar features were identified in typical AVNs. CONCLUSIONS AND RELEVANCE: Arteriovenous nickings do not necessarily involve an arteriovenous compression. Instead, the topology of venous changes suggests a retractile process originating in the intervascular space. These findings have important implications for the understanding of retinal vein occlusions and of cerebrovascular aging.