I’m not a medical expert, but this is the way it’s been explained to me by various ophthalmologists over the years. When you have initial bleeds, the eye tries to repair itself. To maintain blood flow to the retina, the leaking blood vessels (or the retinal cells – I can’t remember) release a growth factor (specifically vascular endothelial growth factor) that prompts the growth of new new micro-capillaries. These new blood vessels are very fine, though, and inclined to rupture as well. This is the stage called proliferative retinopathy. Oftentimes laser treatments target not only actively bleeding vessels but new (and not yet bleeding) growth, to prevent further growth and potential bleeding. Avastin, a drug that targets vascular endothelial growth factor, may also be injected.