AILMENTS

DIABETIC RETINOPATHY

Overview

Patients with diabetes need to get their eyes checked regularly. With India becoming the diabetic capital of the world, managing complications related to diabetes is a major concern. One of the complications is diabetic retinopathy, which is fast gaining importance as a cause of visual impairment among a large population of individuals. If left untreated, it can get worse and cause some loss of vision, or blindness in severe cases.

What is diabetes?

Diabetes is a condition that leads to inadequate control of blood sugar (glucose). In normal persons, blood sugar is tightly regulated by a hormone secreted by the pancreas called insulin. Diabetes mellitus (also called just diabetes) occurs when the level of sugar in blood becomes higher than normal. There are two major types of diabetes

  • Type 1 diabetes that occurs due to a condition that leads to lack of insulin production in the body. This usually begins in children or adolescents or in young adults.
  • Type 2 diabetes that occurs due to relative deficiency of insulin in the body. This type of diabetes is common among the obese and overweight and is usually seen in the middle aged.

Retina

The retina is a curtain of cells that line the back of the eye. It is made up of special light sensitive cells called rods and cones. Light enters the eyes and passes through the lens which focuses the light on to the retina. The light causes electrochemical changes in the retinal cells leading to stimulation of the nerve cells supplying the retina. These nerve cells via the optic nerve carry the visual information to the brain that allows us to see an image. The retina is richly supplied by several tiny blood vessels. These serve oxygen and nutrients to the

cells of the retina. The macula for example is the small part or spot that lies near the centre of the retina.

The macula is where the vision is focuses and is the best point of vision. The central and most important part of the macula is called the fovea. The outer part of the retina is responsible for peripheral vision.

Retinopathy or retinal disease encompasses a variety of pathologies that affect the retina. These can affect vision significantly. In most cases retinopathy is caused due to the damage to the tiny blood vessels in the retina. Retinopathy can be caused by diabetes and high blood pressure. Diabetes may also cause other eye changes and damages including cataracts and glaucoma.

As the blood sugar remains high and uncontrolled among diabetics over several years, the tiny blood vessels in the retina are damaged. In addition the small nerves that take away information from the retinal cells are also damaged due to lack of adequate blood supply to them.

Over several years damage to the small blood vessels lead to

  • Blow-out swellings or ballooning of blood vessels called microaneurysms
  • There may be small leaks from the damaged blood vessels called exudates
  • Some of the small blood vessels may become blocked leading to areas of ischemia or necrosis where cells are deprived of vital oxygen and nutrients and as a result die off
  • Due to blockages, the body develops compensatory measures. New abnormal blood vessels may grow from damaged blood vessels. This is termed proliferative retinopathy. The new blood vessels are fragile and can break and bleed easily giving rise to haemorrhages or bleeding spots
  • Bleedings and damage in the retina may also affect the jelly-like centre of the eye or the vitreous humor. This is called vitreous haemorrhage. Vitreous haemorrhage may also block the light entry on the retina and damage vision.

Types of diabetic retinopathy

  • Retinopathy can affect the macula. This leads to more severe vision loss
  • Retinopathy may also affect peripheral parts of the retina leading to loss of peripheral vision.
  • Broadly retinopathy may also be classified according to stages as

  • Stage 1 - Background retinopathy – this affects almost whole of the retina. There may be microaneurysms, leaks and exudates in various parts of the retina
  • Stage 2 - Pre-proliferative retinopathy – This type of retinopathy shows early signs of blood flow obstruction but there is no evidence of abnormal new blood vessels
  • Stage 3 - Maculopathy refers to affliction of the macula
  • Stage 4 - Proliferative retinopathy – This type of retinopathy occurs when there are damaged blood vessels in the retina leading to abnormal blood vessel growth. These new blood vessels are fragile and may break and bleed easily.

Symptoms

Early diabetic retinopathy seldom causes any symptoms. As the condition progresses there may loss of vision. Over time the condition worsens and leads to blindness. Diabetic retinopathy is the most common cause of blindness in people of the working age group worldwide especially in developing and developed nations.

Some of the symptoms include –

  • Blurring of vision
  • Seeing floaters in the visual field. These are usually exudates or secretions along with cells and blood clots in the vitreous humor that appear in the range of vision
  • There may be flashes of light
  • There may be reduced night vision
  • In severe cases there may be sudden loss of vision.

Risks of diabetic retinopathy –

Retinopathy is one of the more common complications of diabetes. Several factors raise the risk of getting diabetic retinopathy. Some of these include –

  • Duration of diabetes – Longer duration of diabetes usually raises the risk of developing retinopathy. Diabetic retinopathy is rare among persons who have diabetes for less than five years.
  • Poor blood sugar control – Those with persistently raised blood sugar due to inadequate blood sugar control are at a greater risk of diabetic retinopathy.
  • Also high blood pressure raises the risk of developing retinopathy
  • Kidney damage due to diabetes raises the risk of developing retinopathy
  • Smoking, obesity and having a high cholesterol level also raise risk of developing diabetic retinopathy.

Prevention of diabetic retinopathy –

Diabetic retinopathy can be prevented if the blood sugar is well controlled. Blood glucose is controlled by adopting a healthy and balanced diet along with physical activity and medications to lower blood sugar. Apart from blood sugar, blood pressure and blood cholesterol also needs to be tightly controlled. Weight loss and cessation of smoking are important preventive measures. All diabetics should get their eyes checked routinely (annually) to detect early signs of diabetic retinopathy. Treatment can prevent loss of vision and blindness in most cases.

Diagnosis

Diagnosis is made by testing vision and taking digital photographs of the retina. For eye examination drops are put in the eyes to make the pupil as wide as possible. Thereafter instruments are used to look at the retina and take its picture. For retinopathy and the blood vessels a fluorescein angiogram is conducted. A special dye is injected into one of the veins in the arm. This dye then travels to the blood vessels in the eye. When examined with a special camera, the blood vessels light up to reveal abnormalities.

Treatment

Treatment of retinopathy is usually given by laser therapy. Laser treatment is helpful in presence of abnormal blood vessels in the eye. A laser light is focused on the retina to make tiny burns. These help seal the leaks from blood vessels, and stop new vessels from growing further. Several hundred burns may be needed to treat retinopathy. This is also called photocoagulation. Photocoagulation is not usually a painful procedure but may cause some pricking sensation. Laser therapy usually prevents diabetic retinopathy from getting worse. However, laser treatment cannot restore vision that is already lost.

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