Diabetic eye disease

Diabetes can affect the eyes in a number of ways. Over a number of years and especially if the levels of blood sugar, blood pressure and cholesterol are not well controlled, damage to the tiny blood vessels that feed the light seeing part of the eye (the retina) can happen. There are two main ways in which damaged capillaries affect vision. If they become leaky, fluid can escape the blood stream and cause swelling in the centre of the retina (the macula). This is called diabetic macular oedema and can make the vision blurry and sometimes distorted. Additionally, the small capillaries feeding the retina may also become incompetent and stop delivering enough oxygen and nutrients to the retina. As the eye requires a high amount of nutrition, this situation causes abnormal blood vessels to grow. Unfortunately this new vessels are not helpful and can break causing bleeds inside the eye. These bleeds are called vitreous haemorrhage and block light from entering the eye. Untreated new vessels can also attach themselves to multiple parts of the retina and break it, causing a tractional retinal detachment. This is very severe and may lead to permanent vision loss. 

Treatments
Macular oedema can be treated with injections of medicines which help the eye deal more efficiently with leaked fluid from the damaged blood vessels. As the fluid clears the vision improves in most cases. Another modality of treatment is with laser, applying tiny burns to the 
spots in the blood vessels where the fluid is escaping from. Both treatments have advantages and disadvantages which need to be detailed by your doctor during the consultation. 
Proliferative diabetic retinopathy with threatening new vessels is treated with multiple laser burns applied to the far sides of the retina. The aim is to stop these vessels from causing an important bleed or a tractional retinal detachment. This can preserve the central vision at the expense of reducing the field of vision in most people treated. This treatment is very effective and usually definitive but some people may require further treatments. 
Surgery: if the condition has caused a vitreous haemorrhage, this can sometimes clear by itself once the abnormal new vessels have disappeared with laser treatment. In a number of people, the bleed is too dense to clear by itself. Also, it may prevents sufficient laser treatment to be given and stop further bleeds. At this point, a vitrectomy operation becomes necessary. If a tractional retinal detachment appears and begins to threaten the centre of the retina, a complex vitrectomy operation is indicated to prevent further vision loss.