Background
Diabetes is a disease which damages blood vessels in the retina. Diabetic Macular Edema (DME) is caused by leakage of fluid from retinal vessels into the macula. DME is the most common cause of vision loss in diabetics (1).
For over twenty years DME has been treated using laser. While laser treatment is effective in preventing vision loss in most patients, many do not regain vision which has already been lost. Patients with more advanced cases of DME tend to respond poorly to laser treatment (2).
Vascular Endothelial Growth Factor (VEGF) is a substance which occurs naturally in the body. VEGF promotes blood vessel growth and makes retinal blood vessels leaky. Avastin is a drug which blocks VEGF, and was initially used systemically to stop new blood vessels from growing in patients with metastatic bowel cancer. Patients with diabetic retinopathy have abnormally high levels of VEGF in their eyes. Blocking VEGF with Avastin can reduce vascular leakage and lessen macular edema. Reducing macular edema can stabilize or improve vision (3).
Evidence
Avastin was used in a recent study of 78 eyes with DME. All treated eyes had a reduction of macular edema. Vision remained stable in 96% of eyes, and was improved in 55% of eyes. Over a six month period, 21% of eyes required a second injection, and 8% required a third injection (4).
Procedure
The treatment is a brief and typically painless office procedure. Topical anesthesia is applied, and then the medicine is injected into the central cavity of the eye using a fine needle. The injection may cause mild temporary discomfort. More than one treatment is usually required.
Risks
Injections to the eye are relatively safe. Hemorrhage, infection, cataract, and retinal detachment may occur, but are uncommon. Systemic risks of Avastin are rare due to the very small dose and placement of the drug directly into the eye. Systemic risks include elevated blood pressure, stroke, and heart attack.
Alternatives
The only proven treatment to reduce DME is Laser Photocoagulation. Vitrectomy surgery, a procedure in which the vitreous gel, scar tissue, and blood are removed, has been shown to be effective in some patients. A number of medications have been shown to block VEGF, and may prove useful in treating DME in the future.
Comment
Most patients with DME have already lost some vision, and even with laser treatment may lose more. While Avastin was not initially developed to treat DME, it shows great promise in providing stability and improvement in vision. Avastin, while usually safe, has some risks for systemic and ocular complications. These risks should be weighed against the benefit of preservation and improvement of vision.
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