Diabetes affects your eyes when your blood glucose, also called blood sugar, is too high.

In the early stages of the disease, you are unlikely to lose vision due to high blood sugar. People sometimes have blurred vision for a few days or weeks when they change their diabetes care plan or medications. High glucose can change fluid levels or cause swelling of eye tissues. This type of blurred vision is temporary and goes away when glucose levels get closer to normal.

If blood glucose remains high over time, it can damage the small blood vessels at the back of the eye. This damage can start before the diabetes dagnostic is established, when blood glucose is higher than normal but not high enough to be diagnosed with diabetes. Damaged blood vessels can leak fluid and cause edema. New, weak blood vessels may also start to grow. These blood vessels can bleed into the middle part of the eye, lead to scarring or cause dangerously high intraocular pressure.

The most serious diabetic eye diseases start with blood vessel problems. The four eye diseases that can threaten your vision are diabetic retinopathy, diabetic macular edema, glaucoma, and cataracts.

1. Diabetic retinopathy

The retina, the inner layer of the eye, or the vision receptor, senses light and converts it into signals that the brain decodes so that humans are able to see the world around them. Damaged blood vessels can damage the retina, causing a disease called diabetic retinopathy.

In early diabetic retinopathy, blood vessels may weaken, pump or leak fluid that accumulates in the retina. This stage is called non-proliferative diabetic retinopathy.

If the disease worsens, some blood vessels close, causing new blood vessels to grow or proliferate on the surface of the retina. This stage is called proliferative diabetic retinopathy. These abnormal new blood vessels, called neovessels, can lead to serious vision problems.

2. Diabetic macular edema

The part of the retina you need to read, drive and see faces is called the macula. Diabetes can lead to swelling of the macula, which is called diabetic macular oedema. Over time, this disease can destroy the vision in this part of the eye, leading to partial vision loss or blindness. Macular oedema usually develops in people who already have other signs of diabetic retinopathy.

3. Glaucoma

Glaucoma is a group of eye diseases that can affect the optic nerve - the bundle of nerves that connects the eye to the brain. Diabetes doubles the chances of glaucoma, which can lead to vision loss and blindness if not treated early.

4. Cataract

The lenses inside our eyes (crystalline lenses) are clear structures that help us see clearly, but tend to become opaque as we age. People with diabetes are more likely to develop clouding of the lens, called cataracts. People with diabetes may develop cataracts at a younger age than people without diabetes. Researchers believe that high glucose levels cause deposits to build up in the lens.