Diabetes is a disease that occurs when the pancreas does not secrete enough insulin or the body is unable to process it properly. Insulin is the hormone that regulates the level of sugar (glucose) in the blood. Diabetes can affect children and adults.
Patients with diabetes are more likely to develop eye problems such as cataracts or glaucoma, but the principal threat to vision is through diabetic retinopathy. Most patients will have developed some signs of diabetic change in the retina after 20 years.
With time, diabetes affects the blood vessels of the retina, causing impaired circulation and weakness of the vessel walls. In the earliest phase of the disease, ‘background diabetic retinopathy’ – small dot-like haemorrhages – may be visible, but vision is not threatened.
If leakage from blood vessels progresses, the central macular area of the retina becomes swollen and visual symptoms develop. This appearance is described medically as macular oedema and this phase of the disease is known as ‘diabetic maculopathy’. If left untreated, it may permanently damage central vision. Maculopathy is common in Type II diabetes, the form of the disease usually occurring later in life.
Sight may also be threatened by proliferative diabetic retinopathy, in which there is a serious danger of haemorrhage into the vitreous gel which fills the eye. The cause of proliferation is inadequate oxygenation of the tissues of the retina, sometimes referred to as ‘ischaemia’. The retina responds by growing abnormal ‘new vessels’, which are both unhelpful and dangerous and their fragility results in sudden bleeding. This type of retinopathy is often seen in Type I diabetes and, without adequate screening, may go unnoticed until severe haemorrhage occurs.
The most serious form of diabetic retinopathy occurs when proliferation and bleeding result in scarring between the retina and the gel within the eye. Contracting scar tissue can pull the retina away from the eye wall, resulting in permanent blindness.
The best treatment for diabetic retinopathy is preventative. Proper diet and control of the diabetes can greatly impede the progression of diabetic retinopathy. Maculopathy threatening the centre of vision is treated with small numbers of laser burns, which ‘dry up’ the water-logged retina. Injections into the eye (for example steroid treatment) may also be helpful. Proliferative diabetic retinopathy is treated by the application of hundreds, or even thousands, of laser burns to the periphery of the retina. This reduces the volume of sick retina, whilst saving a blood supply for the important central macular area.
Bleeding into the vitreous of the eye may require vitrectomy, a surgical procedure in which the blood-stained gel is safely removed. Bleeding points are treated and laser applied to prevent the development of more abnormal ‘new vessels’. Modern vitrectomy surgery has revolutionized the treatment of severe proliferative diabetic retinopathy, giving hope to the most desperate of cases.