In Vivo Retinal Vein Bypass Surgery in a Porcine Model.

Purpose: To evaluate the feasibility of retinal vein bypass surgery for induced branch retinal-vein occlusion (BRVO) in the living porcine eye.

Methods: Fifteen minipigs were used in the study. Seven days before vascular surgery, hyaluronidase and plasmin were intravitreally injected for induction of posterior vitreous detachment. Aspirin and warfarin were oral administered daily starting 5 d prior to vascular surgery for anti-coagulation. The minipigs were anethetized with an intraperitoneal injection of 300 mg/kg chloral hydrate for intravitreal injection procedure and vascular surgery. Temporary keratoprosthesis vitrectomy was performed, and intraoperative video fluorescein angiography (VFA) was possible. The central and posterior vitreous was removed together with the posterior hyaloid membrane to facilitate vascular maneuvers. BRVO was induced by bipolar diathermy on the vein at the main vein's first branching. Polyimide tubes (50.8-μm internal diameter and 7.6-μm wall thickness) were used as artificial vessels. Vascular manipulation was performed in a bimanual manner. Both end of a prepared tubing was inserted into venous lumen by puncturing and catheterization, and the vein bypass bridging the occlusion was created. Then, the patency of the bypass graft was assessed by intraoperative VFA.

Results: The retinal vein bypass surgery was surgically accomplished in 33% (5/15) of the eyes, and the immediate graft patency was confirmed by intraoperative VFA only in one eye. We observed and recorded fluorescein flow from the branch vein to the main vein through the bypass graft which bridging the occlusive vein segment.

Conclusions: We demonstrated the feasibility of retinal vein bypass for induced BRVO in the living porcine eye, and the immediate graft patency was successfully evaluated by intraoperative VFA. Despite the potential, there are still some significant hurdles in vivo retinal vein bypass surgery, and modification of both surgical instruments and maneuvers is needed for further study.