In the ETDRS (Early Treatment Diabetic Retinopathy Study), the definition of 'clinically significant macular edema' (CSME) includes which of the following criteria?

• A Any macular thickening on OCT > 250 μm irrespective of location
• B Thickening of the retina at or within 500 μm of the center of the macula; hard exudates within 500 μm of center with adjacent thickening; or a zone of retinal thickening ≥ 1 disc area, any part within 1 disc diameter of the center ✓
• C Fluorescein angiographic leakage within 2 disc diameters of the macula regardless of visual acuity
• D Best corrected visual acuity < 20/100 in the presence of microaneurysms within the arcade

Explanation

The ETDRS defined CSME (clinically significant macular edema) using stereoscopic biomicroscopy criteria as any of: (1) retinal thickening at or within 500 μm of the center of the macula; (2) hard exudates at or within 500 μm of the foveal center with thickening of adjacent retina; or (3) a zone of retinal thickening ≥ 1 disc area in size, any part of which is within 1 disc diameter of the foveal center. The ETDRS demonstrated that focal laser photocoagulation reduced the risk of moderate visual loss (≥ 15 letters / 3 lines) by > 50% in CSME. This landmark definition was the standard before OCT-based criteria became predominant. Modern guidelines use OCT-defined center-involving DME.

Reference: Khurana Comprehensive Ophthalmology, 7th ed.

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Written and medically reviewed by the StethoPrep medical team.