Onion ring sign on spectral domain optical coherence tomography in diabetic macular edema: Its evolution and outcomes.

Horizontal, single or multi-layered HCDs on OCT in DM represent intraretinal or subretinal cholesterol crystal precipitates evolving from the hard exudates identical to the "onion ring sign" seen in neovascular AMD. HCDs or CCs depict deranged lipid metabolism, chronic vascular leakage and can lead to substantial visual impairment if the fovea gets involved.