Experimental porcine models of retinal ischemia

Retinal ischaemia resulting from e.g. diabetes, vein thrombosis or arterial occlusion, is one of the major causes of visual impairment and blindness. Although new methods of treatment are being developed, there is still a need for more effective pharmacological forms of treatment. The aim of this work was to develop an appropriate animal model of retinal ischaemia in which the intracellular signalling pathways involved in the development of retinal injury and neovascularization can be studied in the future.
The pig retina was used as it has a morphology and blood supply similar to those of humans. Two different approaches to inducing experimental retinal ischaemia were developed. In Study I, intraocular pressure was elevated, and in Study II, III and IV, an endovascular approach was used to access the retinal vasculature in order to achieve arterial occlusion. The eyes were analysed using indirect ophthalmoscopy, multifocal ERG with fundus imaging, fluorescence angiography and conventional angiography. The porcine model of pressure-induced retinal ischaemia resulted in multifocal ERG changes typical of retinal ischaemia although there may be a confounding problem of pressure-induced damage. Multifocal ERG may be a useful tool to evaluate retinal dysfunction after an ischaemic injury. The retinal circulation could be accessed by transfemoral endovascular catheterization, and the afferent arteries could be occluded using a balloon catheter for temporary occlusion, and a liquid embolic agent or coiling for permanent occlusion. The degree of ischaemia depended on the location of the occlusion. Occlusion of the proximal part of the ophthalmic artery caused little or no ischaemic effect, presumably due to collateral blood supply. Coiling of the distal parts of the ophthalmic artery caused more pronounced ischaemia. Angiographic evidence was found that blood supply to the pig retina may indeed be both ipsilateral and contralateral, due to an interconnecting artery between the eyes. Taken together, the results of this work represent a step in the development of experimental models of retinal ischaemia.