Diabetic Eye Disease Causes

Over many years, high blood sugar and other abnormalities in metabolism found in people with diabetes mellitus may damage the blood vessels in the body. This damage to the blood vessels leads to poor circulation of the blood to various parts of the body. Since the function of the blood is to carry oxygen and other nutrients, this poor circulation causes decreased oxygen delivery to tissues in different parts of the body and subsequent damage to those tissues.


Some of the most sensitive tissues to decreased blood flow and oxygen delivery include the brain, heart, kidneys, and the eyes. Lack of adequate oxygen delivery to these areas causes strokes, heart attacks, kidney failure, and vision loss.


Feet and Lower Legs


The feet and lower legs can also suffer from poor blood circulation and oxygen delivery, resulting in symptoms of:


numbness and tingling;


poor healing of even minor wounds;


ulceration and infection; and,


not infrequently, the need for amputation of a toe, a foot, or the lower leg.
The Retina


The primary part of the eye affected by diabetes mellitus is the retina.


The retina can be thought of as the film in a camera. If the film in a camera is faulty, the resulting picture will be blurry. In a similar manner, if the retina of the eye is swollen, wrinkled, or otherwise structurally damaged, the vision in that eye will be blurry. Depending on the type, location, and extent of damage in the retina, the change in vision will range from minimal to severe and be temporary or permanent.


In people with diabetes mellitus, changes in the walls of the small blood vessels in the retina are caused by blood sugar abnormalities. These small blood vessels may begin to "balloon," forming what are called microaneurysms, as well as leak fluid (called edema) and blood (called dot and blot hemorrhages) into the retina. This process is called background diabetic retinopathy or nonproliferative diabetic retinopathy. If fluid accumulates in the central part of the retina (called the macula) and causes swelling there, the process is called diabetic macular edema. 


As a response to decreased oxygen delivery to the retina, new blood vessels may begin to grow, a process called proliferative diabetic retinopathy. Although new blood vessels may sound like a good thing, considering that the old blood vessels are damaged, the new blood vessels are actually more harmful than beneficial. The new blood vessels are extremely leaky and fragile, potentially leading to bleeding inside the eye (called vitreous hemorrhage) and usually resulting in severe vision loss. If not treated appropriately, this vision loss may be permanent. 


If the new blood vessels are extensive, they may cause scarring inside the eye, resulting in tractional retinal detachments, which is another cause of permanent vision loss. 


In cases of severe proliferative diabetic retinopathy, new blood vessels may grow on the surface of the iris, causing neovascular glaucoma, a particularly severe form of glaucoma.


Many people with diabetes mellitus may notice that their vision becomes blurry when they have fairly large, rapid shifts in their blood sugar levels. This temporary blurring is because the sugar in the blood can diffuse into the lens of the eye and cause it to swell, thus changing the focal point of the eye and resulting in blurring of the vision. Over time, this repeated swelling of this type is thought to damage the lens and cause it to become cloudy, resulting in a cataract. 


The high blood sugar levels may also eventually damage the cells lining the trabecular meshwork toward the front of the eye, where the fluid (called aqueous humor) flows out from within the eye. When these cells are damaged, the trabecular meshwork cannot function correctly. If the trabecular meshwork does not function correctly, the fluid cannot flow out of the eye properly and the pressure inside the eye can increase. This high pressure inside the eye can damage the optic nerve and cause permanent vision loss. This process is called glaucoma.