Carol M Lee, MD
As defined by the Early Treatment Diabetic Retinopathy Study (ETDRS), diabetic macular edema (DME) is considered clinically significant (CSME) and should be treated if slit-lamp biomicroscopy with a hand-held or contact lens reveals any one of the following 3 conditions:
- Macular thickening ≤500 microns from the center of the macula
- Hard exudates ≤500 microns from the center of the macula if the adjacent retina is thickened
- Zone(s) of retinal thickening ≥1 disc area in size, any part of which is ≤1 disc diameter from the center of the macula
Fluorescein angiography (FA) should be obtained once a treatment decision is made based upon the findings on slit-lamp biomicroscopy. FA is useful for delineating the foveal avascular zone (FAZ) and assessing macular perfusion. FA is also used to determine whether to use focal or grid laser photocoagulation. Focal leakage is less common than diffuse leakage. Patients should be instructed that the goal of laser photocoagulation treatment is to stabilize, not improve, vision.
Using the ETDRS protocol, focal laser treatment is performed with a 100-micron spot size for 0.1 seconds duration. Use the green-only wavelength; the red wavelength may be used in selected areas. Start with the power set to 100 milliwatts, increasing slowly by 20-30 milliwatts until a light-intensity burn is produced. Do not try to close microaneurysms, and do not treat within the FAZ.
Grid laser treatment is performed on areas of diffuse leakage with 100-, 150-, or 200-micron spots for 0.1 seconds duration. Use the green-only wavelength; the red wavelength may be used in selected areas. Start with the power set to 100 milliwatts, increasing slowly by 20-30 milliwatts until a light-intensity burn is produced. Place spots in a grid pattern, but do not treat within the FAZ.
Modified grid treatment applies grid laser to areas of diffuse leakage, with focal laser to areas of discrete local leakage outside the grid area.
If CSME persists at the 3- to 4-month followup visit, supplemental treatment is recommended. Repeat FA, and use focal, grid, or modified treatment as needed. Most patients need more than 1 treatment to reduce CSME.
If CSME persists despite laser treatment, if there is extensive diffuse leakage, or if there are extensive hard exudates, consider steroid treatment. Steroids may be administered by intravitreal injection or by implant.
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