Generality
Diabetic retinopathy is a late complication of diabetes. The condition, in fact, normally occurs after years of the onset of diabetic disease, especially when it is not treated properly.
Diabetic retinopathy usually affects both eyes. At first, the disease can cause only minor vision problems or be asymptomatic, but its progression can cause blindness, which in many cases cannot be reversed. For this reason, patients with diabetes are recommended a thorough eye examination at least once a year, to monitor the course of diabetic retinopathy. If the disease is detected in time, it can be effectively treated by photocoagulative laser therapy. Since the symptoms of diabetic retinopathy occur, the condition can be very difficult to manage.
Causes
How diabetes can damage the retina
The retina is the layer of photosensitive cells that lines the back of the eye. This membrane is responsible for converting light stimuli into electrical impulses, which the optic nerve transmits to the brain. To work effectively, the retina needs a constant supply of blood, which it receives through a network of small blood vessels.
Uncontrolled hyperglycemia can cause transient visual disturbances and, over time, can damage the blood vessels supplying the retina. These capillaries start pouring fluids and lipids, causing edema (swelling) and subsequent retinal ischemia. These pathological phenomena are typical of non-proliferative diabetic retinopathy (NPDR). If the eye problems associated with diabetes are neglected, the condition may progress to proliferative diabetic retinopathy (PDR). This is characterized by the growth of new blood vessels (neovascularization), which can damage the retina and cause its detachment. High levels of glucose in the blood can also have consequences at the level of the lens: cataracts (opacity of the lens) are favored by diabetes. Keeping blood glucose and blood pressure under control, as well as undergoing regular eye examinations, are the key factors on which to intervene for the prevention of diabetic retinopathy and its progression.
Non-proliferating diabetic retinopathy
Non-proliferative diabetic retinopathy (NPDR) represents the first and least aggressive stage of the disease. NPDR is characterized by the presence of microaneurysms, hemorrhages, exudates and thromboses. The most serious complication is macular edema. Sometimes, deposits of cholesterol or other fats from the blood can infiltrate the retina (hard exudates). The first ocular changes that are reversible and do not threaten central vision are sometimes called simple retinopathy or background retinopathy.
Proliferating diabetic retinopathy.
Proliferating diabetic retinopathy (PDR) is the most serious and dangerous form of the disease: it occurs mainly when many of the blood vessels supplying the retina become occluded, resulting in retinal ischemia. In an attempt to supply a sufficient quantity of blood, the growth of new retinal capillaries (neovascularization) is stimulated; however, these neovases are abnormal, fragile and do not provide the retinal surface with proper blood flow.
Phases of the disease
The signs and symptoms of diabetic retinopathy become progressively more severe as the condition evolves through the following phases:
- Mild non-proliferative diabetic retinopathy: during the initial stages of retinopathy, the damage is limited to the formation of tiny extroflexions (microaneurysms), caused by the weakening of the walls of the small blood vessels of the retina. Although these can spill liquids and blood, they usually do not affect vision.
- Moderate non-proliferative retinopathy: when retinopathy progresses, some of the blood vessels supplying the retina close completely, while others may expand.
- Severe non-proliferative retinopathy : a higher number of blood vessels is occluded and the resulting retinal ischemia deprives the areas of the oxygen retina. To compensate for this event, neovascularization begins, in an attempt to restore adequate blood supply to deficient retinal areas. However, the newly formed blood vessels do not develop properly, are unstable and prone to bleeding.
- Proliferative retinopathy : new abnormal blood vessels begin to grow on the surface of the retina. The newly formed vessels are fragile and break easily, also causing bleeding that can fill the posterior chamber of the eye occupied by the vitreous body (emovitreo). Over time, the discharge of blood or liquids can lead to the formation of scar tissue, which can lift the retina from its normal position. This pathological phenomenon, known as detachment of the tractional retina, can cause a darkening of vision, myopia ("flying flies") and, if untreated, blindness.
At each stage, the blood or the liquid part of it can flow into the macula, a small and highly sensitive part of the retina (the macula allows details to be distinguished during activities such as reading or writing). The accumulation of fluid in this area (known as macular edema) can cause progressive damage to nerve fibers and the consequent deterioration of visual function. This phenomenon is one of the most common causes of vision loss in diabetic patients.
Risk factors
The risk of developing diabetic retinopathy is related to diabetes mellitus, both type 1 (insulin-dependent, in which the body does not produce insulin) and type 2 (non-insulin-dependent).
Diabetes is a chronic disease that affects the body's ability to effectively produce or use insulin to control blood sugar levels. In its course, the pathology involves numerous apparatuses (cardiovascular, renal, nervous, extremities of the lower limbs etc.). At the ocular level, the effects of diabetes can affect the lens (cataract) and the retina. In diabetic patients, blood glucose, which is the concentration of glucose in the blood, is higher than normal. Although glucose is a vital source of energy for cells, a chronic rise in blood sugar (termed hyperglycemia) causes damage throughout the body, including the small blood vessels that supply the eyes.
Several factors can influence the development and severity of diabetic retinopathy, including:
- Duration of diabetes: the risk of developing diabetic retinopathy or progressing to its progression increases with time. After 15 years, 80% of symptomatic subjects with type 1 diabetes have a varying degree of diabetic retinopathy. After about 19 years, up to 84% of patients with type 2 diabetes can potentially present the disease.
- Blood glucose level control: a diabetic patient with persistent hyperglycaemia has a higher risk of developing this ocular complication. Blood glucose control is one of the key factors on which action can be taken: lower blood glucose levels can delay the onset and slow the progression of diabetic retinopathy.
- Blood pressure: effective blood pressure control reduces the risk of retinopathy progressing, preventing deterioration of visual acuity. Hypertension damages blood vessels, increasing the chances of developing eye disorders. Therefore, taking measures to prevent high blood pressure, such as stopping smoking and reducing the amount of salt in the diet, can help reduce the risk of developing retinopathy.
- Levels of lipids in the blood (cholesterol and triglycerides): elevated levels of lipids in the blood can lead, at the retinal level, to a greater accumulation of exudates and to the formation of deposits constituted by fibrin and lipids (which escape from the dilated capillaries), as a consequence of retinal edema. This condition is associated with a higher risk of experiencing moderate visual loss.
- Pregnancy: a diabetic woman in pregnancy may present an increased risk of developing diabetic retinopathy. If the patient already has the disease, it may progress. However, these changes can be reversed after delivery or there may be no long-term progression of the disease.
Symptoms
To learn more: Symptoms Diabetic retinopathy
During the initial stages, diabetic retinopathy does not cause any signs of early warning. The patient, therefore, may not be aware of the disease until the later stages, as changes in vision may be evident only when the retina is severely damaged. In the proliferative phase of diabetic retinopathy, bleeding can induce reduced vision and blurred vision.
As the disease progresses, the symptoms of diabetic retinopathy may include:
- Appearance of small mobile bodies (black dots, dark spots or streaks) that fluctuate in the visual field (floaters);
- Blurring of sight;
- Night vision reduction;
- Empty or dark areas in the visual field;
- Difficulty in color perception;
- Sudden reduction in visual acuity.
Diabetic retinopathy usually affects both eyes and - if not correctly diagnosed and treated - can induce blindness. Therefore, it is very important that diabetic retinopathy is identified at an early stage and, if necessary, an appropriate therapeutic protocol is established. Careful monitoring aims to reduce the risk of vision loss in people with diabetes.
Clinical signs of non-proliferative diabetic retinopathy (NPDR)
Non-proliferative diabetic retinopathy can cause:
- Microaneurysms: small extractions of the wall of the capillaries of the retina, which often cause the pouring of fluids.
- Retinal hemorrhages: small blood stains located in the deeper layers of the retina.
- Hard exudates: deposits of cholesterol or other plasma lipids that escape from dilated capillaries and from microaneurysms (they are associated with retinal edema).
- Macular edema: swelling of the macula caused by the leakage of liquids from the blood vessels into the thickness of the retina. Macular edema is the most common cause of loss of visual function in diabetes.
- Macular ischemia: the small blood vessels (capillaries) that supply the retina may become blocked. This determines the blurring of vision, as the macula no longer receives enough blood to function properly.
Clinical signs and possible complications of proliferative diabetic retinopathy (PDR)
PDR can cause more severe vision loss than non-proliferative diabetic retinopathy, as it can affect both central and peripheral vision:
- Vitreous hemorrhage (emovitreo): the new blood vessels can spill blood into the vitreous humor (the gelatinous substance that fills the inside of the eye), preventing light from reaching the retina. If bleeding is limited, the patient may see only a couple of dark spots or loose bodies. In severe cases, the bleeding can fill the vitreous cavity and totally compromise vision (the patient could only perceive light and darkness). Emovitreo alone usually does not cause permanent vision loss. The blood, in fact, tends to be reabsorbed within a few weeks or months and the vision can be restored to the previous level (unless the macula has been damaged).
- Detection of the retinal traction: the abnormal blood vessels associated with diabetic retinopathy stimulate the growth of scar tissue, which can detach the retina from its normal position. This could cause vision of floating spots in the visual field, flashes of light or severe vision loss. The greatest alteration of visual function can occur if the retinal detachment involves the macula.
- Neovascular glaucoma: if a number of retinal vessels are occluded, neovascularization can occur in the anterior part of the eye. In this condition, an increase in pressure in the eye (glaucoma) may occur, due to the alteration of normal blood flow. Persistent ocular hypertension can severely damage the optic nerve.
- Blindness. Advanced proliferative diabetic retinopathy, glaucoma or both can lead to complete loss of vision.
Diagnosis and Treatment of Diabetic Retinopathy »
