Diabetic Macular Edema
Diabetic Macular Edema (swelling) is the most common cause of vision loss in diabetics. The incidence is roughly proportional to the duration of diabetes. In other words, 10% of patients with 10 years of diabetes develop macular edema, and 20% of patients with 20 years of diabetes develop macular edema. Diabetics who maintain close to normal blood sugars, rarely develop macular edema.
Diabetes causes damage to retinal capillaries (very small vessels) through loss of their supporting cells--pericytes. Once the retinal capillaries are damaged, microaneuryms form. Then the vessels leak and the retina swells.
Focal laser treatment reduces the risk of vision loss of patients with diabetic macular edema and causes some improvement in vision in 50% of patients.
Patients with diabetic macular edema are usually evaluated with a detailed retinal examination. If the evaluating physician sees macular edema (retinal swelling), he or she may order an optical coherence tomography scan of the retina. Optical coherence tomography measures the retinal thickness and shows microstructural retinal abnormalities that are sometimes not visible to the examining physician.
In addition, to find the exact location of leaky retinal vessels, and to differentiate between focal edema from discreet retinal abnormalities and diffues edema from diffuse leakage from retinal vessels. Patients, like the one pictured to the right, with focal leakage do better with laser than those with diffuse leakage.
There are two main options for treatment of patients with diabetic macular edema. Focal laser is most helpful in eyes with discreet leaky spots in the retinal vessels. Focal laser has been tested in large studies where treated and untreated eyes were compared. Most diabetics with macular edema have an average of 2 to 4 focal lasers every 10 years. The benefit of focal laser is reducing the risk of vision loss and improving vision. The risk of focal laser is the very rare possibility of a scar growing from a laser spot. This probably only happens to about 1 in 1000 patients. Also, a patient has to be able to hold reasonably still, since the laser is applied close to the central vision.
Intravitreal injections are very effective treatments for diabetic macular edema. Intravitreal steroids and vascular endothelial growth factor inhibitors are both effective, in the short term, at reducing macular edema. The benefit of these treatments is there rapid effect at reducing swelling. They are also very useful for treating patients who have swelling of the very center of the retina where laser treatment might be more dangerous. Also, in eyes where fluorescein angiography shows diffuse leakage from retinal vessels without much focal leakage, injections are probably more effective than laser. The downside to intravitreal injections is there limited duration of effect. Long-acting intravitreal steroids can cause resolution of edema for 6 months. Vascular endothelial factor inhibitors only work for 1 to 3 months. Also, many insurance companies at the time of this writing (July 2008) do not pay for intravitreal injections for diabetics.
Treatment with laser and/or intravitreal injections is very effective at reducing the risk of vision loss in diabetics. Once patients have lost vision from diabetic macular edema, the chance of improving vision with therapy is only about 50%.
Patients with other systemic problems sometimes have diabetic macular edema resistant to treatment:
- High Blood Pressure
- Carotid Insufficiency
- Congestive Heart Failure
- Kidney Failure
Patients with other eye probems can also be resistant to therapy:
- Macular Pucker
- Vitreo-macular traction
- Retina vein occlusion
- Wet age related macular degeneration