High blood sugar in diabetes causes the lens of the eye to swell, which changes your ability to see.
To correct this kind of eye problem, you need to get your blood sugar back into the target range (90-130 milligrams per deciliter or mg/dL before meals, and less than 180 mg/dL one to two hours after a meal). It may take as long as three months after your blood sugar is well controlled for your vision to fully get back to normal. Blurred vision can also be a symptom of more serious eye problem with diabetes. The three major eye problems that people with diabetes may develop and should be aware of are  cataracts  glaucoma  retinopathy
What is Retina?
The retina is a group of specialized cells that convert light as it enters though the lens into images. The eye nerve or optic nerve transmits visual information to the brain.
It is one of the vascular (blood-vessel related) complications related to diabetes. This diabetes eye problem is due to damage of small vessels and is called a “microvascular complication.” Kidney disease and nerve damage due to diabetes are also microvascular complications. Large blood vessel damage (also called macrovascular complications) includes complications like heart disease and stroke.
The microvascular complications have, in numerous studies, been shown to be related to high blood sugar levels. You can reduce your risk of these eye problems in diabetes complications by improving your blood sugar control.
Your retina can be badly damaged before you notice any change in vision.
Most people with nonproliferative retinopathy have no symptoms. Even with proliferative retinopathy, the more dangerous form, people sometimes have no symptoms until it is too late to treat them. For this reason, you should have your eyes examined regularly by an eye care professional.
People with type 1 diabetes :
They rarely develop retinopathy before puberty.
People with type 2 diabetes :
They usually have signs of eye problems when diabetes is diagnosed. In this case, control of blood sugar, blood pressure, and blood cholesterol with diabetes have an important role in slowing the progression of retinopathy and other eye problems.
Types of Retinopathy in Diabetes:
I. Background retinopathy – Sometimes the blood vessel damage exists, but there is no vision problem. This is called background retinopathy. It’s important to carefully manage your diabetes at this stage to prevent background retinopathy from progressing to more serious eye disease. In nonproliferative retinopathy, capillaries in the back of the eye balloon and form pouches. Nonproliferative retinopathy can move through three stages (mild, moderate, and severe), as more and more blood vessels become blocked. Although retinopathy does not usually cause vision loss at this stage, the capillary walls may lose their ability to control the passage of substances between the blood and the retina. Fluid can leak into the part of the eye where focusing occurs, the macula. When the macula swells with fluid, a condition called macula edema, vision blurs and can be lost entirely. Although nonproliferative retinopathy usually does not require treatment, macular edema must be treated, but fortunately treatment is usually effective at stopping and sometimes reversing vision loss.
II. Maculopathy – In maculopathy, the person has developed damage in a critical area called the macula. Because this occurs in an area that is critical to vision, this type of eye problem can significantly reduce vision.
III. Proliferative retinopathy – New blood vessels start to grow in the back of the eye. Because retinopathy is a microvascular complication of diabetes, a disease of small vessels, this type of retinopathy develops because of an increasing lack of oxygen to the eye from vascular disease. Vessels in the eye are thinned and occluded and they start to remodel. In this form, the blood vessels are so damaged they close off. In response, new blood vessels start growing in the retina. These new vessels are weak and can leak blood, blocking vision, which is a condition called vitreous hemorrhage. The new blood vessels can also cause scar tissue to grow. After the scar tissue shrinks, it can distort the retina or pull it out of place — this is called retinal detachment.
Risks factors that can worsen the occluded vessels.
I. Smoking cessation
II. High blood pressure control
III. Cholesterol management
IV. Blood sugar control must take place in order to stop the progression of new vessels from forming into the orbit of the eye.
These are fragile vessels that can bleed and eventually cause a clot to form in the orbit, which scars and causes detachment of the retina. This eventually leads to irreversible vision loss.
To prevent retinopathy with diabetes:
I. People with type 1 diabetes should have a dilated eye exam by an ophthalmologist or optometrist within three to five years after diagnosis.
II. People with type 2 diabetes should have a dilated eye exam by an ophthalmologist or optometrist shortly after diagnosis.
III. Annual eye exams should be done with both type 1 and type 2 diabetes by an ophthalmologist or optometrist; more frequently if necessary.
IV. When considering pregnancy, women with a history of diabetes should have an eye exam prior and during pregnancy. This does not pertain to women with gestational diabetes.
To prevent eye problems in diabetes, you should:
I. Control your blood sugar
II. Control high blood pressure
Huge strides have been made in the treatment of diabetic retinopathy.
Treatments such as scatter photocoagulation, focal photocoagulation, and vitrectomy prevent blindness in most people. The sooner retinopathy is diagnosed, the more likely these treatments will be successful. The best results occur when sight is still normal.
Here the eye care professional makes tiny burns on the retina with a special laser. These burns seal the blood vessels and stop them from growing and leaking.
Scatter Photocoagulation (also called panretinal photocoagulation):
Here the eye care professional makes hundreds of burns in a polka-dot pattern on two or more occasions. Scatter photocoagulation reduces the risk of blindness from vitreous hemorrhage or detachment of the retina but it only works before bleeding or detachment has progressed very far. This treatment is also used for some kinds of glaucoma.
Side effects of scatter photocoagulation are usually minor. They include several days of blurred vision after each treatment and possible loss of side (peripheral) vision.
Here the eye care professional aims the laser precisely at leaking blood vessels in the macula. This procedure does not cure blurry vision caused by macular edema. But it does keep it from getting worse.
When the retina has already detached or a lot of blood has leaked into the eye, photocoagulation is no longer useful. The next option is vitrectomy, which is surgery to remove scar tissue and cloudy fluid from inside the eye. The earlier the operation occurs, the more likely it is to be successful. When the goal of the operation is to remove blood from the eye, it usually works. Reattaching a retina to the eye is much harder and works in only about half the cases.