Diabetes and eye have a very strong relation. Diabetes can affect the eyes and vision in a number of ways. The high blood glucose, can damage many parts of the body, such as the heart, blood vessels, brain, and kidneys (as commonly known). Diabetes can affect the eyes also and in a similar fashion.

The parts of the eye which are affected by diabetes are: -
Retina - The retina is the lining at the back of the eye. The retina's job is to sense light coming into the eye.
Vitreous - The vitreous is a jelly-like fluid that fills the back of the eye, in front of the retina.
Lens - The lens is at the front of the eye. It focuses light on the retina.
Optic nerve - The optic nerve is the eye's main nerve to the brain.
Eye muscles.

Retinal damage:
Retina damage happens slowly. Diabetes affects the small vessels of the retina in the eye. First, these tiny blood vessels swell and weaken causing leakage. Severe damage can present as bleeding in the eye. Initial retinal changes might not cause and visual changes, but later on can present as blurring of vision.

Symptoms seen when retina starts getting involved are :
Blurry or double vision
Rings, flashing lights or blank spots
Dark or floating spots
Trouble seeing things out of the corners of your eyes

Treatment for this is retinal laser in mild cases and surgery in severe retinopathy.
Lens damage:
Cataract (saphed motia) is a normal aging phenomenon. In patients with diabetes are 60% more likely to develop this eye condition in younger age. Treatment for this is surgery by Phacoemulsification (sitchless cataract surgery).

Optic nerve damage:
Glaucoma (kala motia) if not treated can damage the optic nerve and cause permanent decrease in vision. Patents with diabetes are 40% more likely to suffer from glaucoma than people without diabetes. Treatment for glaucoma is medical and surgical depending on the severity.

Eye muscles and nerves:
Occasionally paralysis of one of the eye muscles can cause squinting of the eye (mostly outwards) or can cause facial nerve palsy, which presents as incomplete closure of the eye. Mostly the nerve and muscle involvement recovers in six months.

How can the effect of diabetes are reduced on eye:
A strict diabetic control
6 monthly complete check-up of the eye
Regular exercise
Weight control
Control of other chronic diseases like hypertension, high blood cholesterol etc

Eyes are the windows to the effect of diabetes on all body organs like heat, brain, kidney, liver etc. The amount of damage in the eye is symmetrical to the effect on all the other body organs. So a strict diabetic control is very important.