The most serious eye complications for people with diabetes are forms of retinopathy, the enlargement, breakage, or leaking of tiny blood vessels in the eye, which can spill blood into the eyeball and threaten vision.
Diabetic retinopathy is an important cause of blindness in industrialized countries and a common complication of Type 2 diabetes.
In the United States it is the leading cause of newly diagnosed cases of Type 2 diabetes in people 20 to 74 years of age.
From 2005 to 2008...

• 5 per cent of people over 40 years of age in the United States had some degree of diabetic retinopathy, and
• 4 per cent of them, or 655,000, had advanced retinopathy leading to loss of vision.
  

The condition is insidious, and individuals can have mild cases for years before vision loss becomes apparent.
Diabetes affects all the blood vessels in the body, causing them to lose much of their ability to conduct blood to and from the tissues.
In Type 2 diabetes blood vessels in the retina, the back of the eye where a picture of what is being seen is formed, are unable to deliver a sufficient amount of blood, floaters and blind spots can develop and, in time, the condition can worsen to total blindness.
Investigators at the Institute for Clinical Research and Development in Mainz, Germany, examined the eyes of pre-diabetics and non-diabetics to compare the changes, if any, that might exist in the blood flow to the eyes with those seen in people with full-blown Type 2 diabetes.
Their study, published in January 2012 in the Journal of Diabetes Science and Technology, included 54 volunteers, classified into three groups:

• non-diabetic, insulin-sensitive volunteers with a body mass index of less than 28,
• non-diabetic, insulin-resistant volunteers with a body mass index of at least 28, and
• individuals with a diagnosis of Type 2 diabetes.
  

The walls of arteries in the eyes of those in the first group had significantly more open space in which to carry blood than those in the third group.
Those with the highest insulin resistance showed the narrowest blood vessels and blood flow, and both went up steadily with increasing insulin sensitivity.
From this research it was concluded the development of insulin resistance was an important factor in the deterioration of blood flow to the arteries in the eye.
According to the National Institute of Health in the United States, the natural history of diabetic retinopathy is divided into four stages...
Stage one is the mild, or non-proliferative, stage.
In the first stage there are tiny outpouchings in the retinal arteries, like little balloons.
In the second, or moderate, non-proliferative stage, blockages are seen in retinal arteries, slowing down blood flow to the eye.
The third stage is severe non-proliferative retinopathy, in which the retina sends out signals for the blood vessels to create new branches.
The fourth and final stage is proliferative retinopathy, in which new blood vessels grow, or proliferate.
The new blood vessels are abnormally frail, and their breakage causes bleeding into the eye, which can lead to blindness.
Controlling your blood sugar levels, blood pressure, and blood cholesterol levels, can all help to prevent blindness.
Diabetic patients should have their eyes checked at least annually, or more frequently if recommended by their doctor..