How does diabetes affect your eye sight?

Vision changes. Many ways, but fluctuating sugars can even blur vision just due to osmotic changes in the lens from sugar byproducts. Retinal hemorrhage and edema can also decrease vision. Cataracts form faster. Regular eye exams are key to preventing vision loss.
Depends on control. If sugar kept within normal limits, eyes are often stable, but with high sugar, you become more near sighted (can't see far away as well). Then the blood vessels fail to function leaking fluid and cells or making a bubble (microaneurysm). That is the earliest stage of retinopathy. All of the nerves that move the eye can be weakened or paralyzed also.
Lowered vision. Diabetes, when poorly controlled, can cause the blood vessels in the retina at the back of the eye, to dilate, bleed and scar which can have profound effects on vision. All diabetes should have a yearly eye examination because much of these changes are treatable.
Diabetic Retinopathy. Diabetes can cause a wide array of visual problems, especially if uncontrolled for prolonged time periods. Cataracts may result from diabetes but the more significant problems to attend to relate to retinal health. Uncontrolled diabetes damages small vessels (arterioles and capillaries) as sugar residues impair their integrity and increase their permeability. This results initially in small retinal hemorrhages and capillary “blowouts” called microaneurysms. These damaged capillaries not only let blood seep into the retina, but also allow the plasma fluid (within which red blood cells live) to seep into the macula, the central portion of the retina, responsible for fine detail vision. Accumulation of this fluid in the macula is called macular edema and the presence of this condition leads to significant visual distortion and blur. Up to this point, these changes are called non-proliferative, background diabetic retinopathy. More severe problems occur later when the eye produces “new blood vessels” (neovascularization) to replace the damaged capillaries and arterioles. Unfortunately, even though the eye wants to correct the problem at hand, the “new vessels” are fragile and tend to break easily and bleed. They actually grow out from the surface of the optic nerve and retina into the vitreous humor, so eye movement may disturb them, bringing about vitreous hemorrhage. It is not easy to see through an eye full of blood. Even worse than this, though, is that these blood vessels tend to contract and bring the retina up with them, causing a tractional retinal detachment. These changes are now known as proliferative diabetic retinopathy (because of the proliferation of new blood vessels) and are associated with progressive, severe vision loss. Luckily, we have excellent treatment options including laser, intraocular pharmaceutical injections and surgery for all stages of diabetic retinopathy (except, perhaps, for end stage, ischemic disease, where so little normal blood flow remains, that intervention is frequently futile). The key to diabetes, however, is prevention and earlier intervention has been proven time and again, through clinical trials and clinical experience, to afford the best visual prognosis in all cases. So if you have diabetes, it is extremely important to maintain close follow-up with an ophthalmologist and vitreoretinal specialist and be examined at least twice yearly.
See a retina special. A retina specialist is the correct person to treat the different kinds of diabetic retinopathy. For diabetic macular edema: laser, eye injections of medicine (anti-vegf and steroids). For proliferative diabetic retinopathy: laser, eye injections of medicine. For vitreous hemorrhage: vitrectomy surgery with laser. For tractional retinal detachment: vitrectomy, with laser and membrane peeling.