Diabetic Retinopathy

Retina is the inner most layer of the eye ball which contains the system of absorbing light and producing light stimuli which then converges on the optic nerve to be transmitted to the brain. Retina is a highly metabolically active tissue consuming a large amount of Oxygen. So it has a rich vascular supply in health.

In diabetes the long term exposure to high blood sugar damages the retinal capillaries. The inner layer of the capillaries, i.e the basement membrane becomes thickened leading to blockade. The pericytes ,contractile cells that surround the capillary endothelium become less in number causing the capillaries to dilate (microaneurysms)  and then rupture (dot hemorrhages).Weakened capillary walls allow leakage of lipid rich fluid out on to the retina.(Hard exudates)

These changes happen during the Non proliferative stages of DR. Depending on the severity of changes and their distribution on the retina there is mild, moderate or severe stages.   

As the disease progresses and a significant area of retinal tissues become ischemic (damaged due to lack of oxygen) those tissues release substances to stimulate growth of new vessels. This could be considered as an attempt to supply oxygen to the damaged areas. But these erroneous vessels do not fulfill the expected duty. Instead, they grow along the retina and sometimes grow vertically into the vitreous gel in the cavity of the eye globe. These vessels are fragile and tend to bleed easily into the retina or vitreous causing disturbance of vision and sometimes profound loss.

In some individuals with or without the above changes the central part of the retina becomes the main area affected. This central part called macula becomes swollen causing the images to be distorted. This is called Diabetic Macular Edema