Figure 2. Porcine retinal flat mounts. Pieces of fresh, unfixed, porcine retina in PBS, as seen in a dissecting microscope. Vessels are filled with red blood cells. A–D: Many arteriovenous crossings at different distances from the optic nerve head (located at the bottom of each image) are visible. The veins are somewhat thicker than the arteries. E–F: Arteriovenous crossing in a flat mounted porcine retina imaged with differential interference contrasts (DICs). E: Focus on the thick-walled artery. F: Focus on the vein that is crossing above the artery.