- Presence of clinically significant macular edema, with visual acuity less than 0.4 corrected to EDRS scale, which is refractory to at least two sessions of laser photocoagulation, defined as: A) Thickening of the retina at or within 500 μm of the center of the macula. B) Hard exudates at or within 500 μm of the center of the macula, if associated with thickening of the adjacent retina. C) A zone or zones of retinal thickening 1 disc area or larger, any part of which is within 1 disc diameter of the center of the macula.