Dynamic Non-Contrast Imaging of Occult Retinal Collateral Circulation Patterns Using the Retinal Functional Imager (RFI)

Abstract

Purpose: : To dynamically image, characterize, and catalog the variety occult retinal collateral circulation patterns revealed in normal subjects and in patients with ocular disease using the Retinal Functional Imager(RFI).

Methods: : Normal subjects and patients with ocular disease referred to the Retina Center of The New York Eye & Ear Infirmary, New York, USA. were imaged with the RFI (Optical Imaging,Ltd, Rehovot, Israel) to characterize dynamic blood flow parameters and study microcirculatory patterns. The RFI consists of a modified digital fundus camera with a stroboscopic flash delivery system. Studies consist of high-speed sequences of 8 red-free fundus images captured within 125 ms. Sequences allow velocity and flow analysis of individual retinal vessels within each frame and can be reviewed as video loops which highlight flow directions and pattern.

Results: : Twenty eight eyes of 21 patients were studied. (8 eyes of six normal subjects and 20 eyes of thirteen patients with known ocular diseases). Review of video RFI sequences identified four distinct dynamic flow patterns of retinal collateral circulation: 1. "Looped" arteriovenous anastomotic collateral vessels, which are characterized by a link joining the endings of the adjacent artery and vein and has an appearance of a loop. 2. "Vertical" arteriovenous anastomotic collateral vessels, which cross the horizontal raphe connecting the superior and inferior vascular arcades. 3. "H-shaped" horizontal arterovenous anastomotic collateral vessels, which are characterized by connection between two adjacent vessels (artery and vein) in the middle of their extent instead of at the ends liked the "looped" pattern 4. "Retinal-Cilioretinal" anastomotic collateral vessels, which are characterized by the connection between a cilioretinal artery and retinal blood vessels.

Conclusions: : This is the first report of occult collateral retinal vascular patterns imaged dynamically without contrast agents, using the RFI. While some of these patterns of retinal collateral circulation may be detected with conventional fluorescein angiography, their presence in normals has not been noted and they have been observed in pathological eyes only when they are large and mature. The ability to non-invasively detect anomalous microvascular changes as described here may enhance our understanding of retinal vascular plasticity and help our management of retinal vascular disease.

Keywords: vascular occlusion/vascular occlusive disease • imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound) • retinal neovascularization