What is diabetic macular oedema?
The retina is a thin tissue at the back of the eye, which works bit like film in a camera. The word ‘macula’ refers to center of the retina. Being central, macula provides detailed sharp vision, especially near vision such as reading, knitting etc. Patients with diabetes develop leaky blood vessels with hardening of blood vessel wall. When the blood vessels cause leakage in the macula it causes waterlogging in macula called macular oedema. Since the macula is responsible for detailed sharp vision, macular oedema causes blurred vision.
Why does DMO occur?
Diabetes affects blood vessels through out the body. There is hardening of the blood vessels causing decrease circulation and increased leakage. The reduction in circulation also causes lack of oxygenation of tissue. When this affects blood vessels in macula there is collection of fluid and waterlogging causing blurred distorted vision. Patients with poorly controlled diabetes, high blood pressure, smoking, high cholesterol and kidney disease are at higher risk of developing DMO.
What tests are required?
Specialized photographs of the retina are carried out to help decide severity of oedema and state of circulation in the macula.
1. Fundus fluorescein angiography – in this test a dye is injected in the arm and photographs are taken of the dye as it passes through the blood vessels at the back of your eye.
2. OCT retinal scan – It is a simple test which uses light beam to build up a detailed picture of the retina. The figure 1 shows macular oedema caused by leakage of fluid.
What are the treatment options?
1. Laser treatment to macula: This involves applying laser burns in the macular region. It is carried out as an outpatient procedure.
2. Injection of anti-vascular endothelial growth factor (anti-VEGF) drugs in the eye: The anti-VEGF drugs works on leaky blood vessels to help reduce fluid in the macula. Lucentis, Eylea and Avastin are the drugs available in this category. Injections are given in an outpatient setting under local anaesthesia. One injection is given every month for first three months. Thereafter monthly assessment continues during which further injections may be needed.
3. Injection of Steroid in the eye: Ozurdex is a very small steroid implant, which is injected in the eye under local anaesthesia. It slowly releases drug into the eye, hence the effect of treatment lasts 3-4 months. The treatment can be repeated. The new drug Iluvien works similarly but once injected, the implant lasts for 3 years.
What are the risks of treatment?
Generally speaking benefits outweigh the risks. An injection carries a small risk (0.3%) of infection in the eye (endophthalmitis). With Ozurdex and Iluvien treatment the main risks are glaucoma (increased pressure in the eye) and cataract (cloudy lens). With Lucentis injection there is a small risk (1-2%) of cardiovascular events such as heart attack and stroke.