To describe the features of cotton wool spots (CWSs) in diabetic retinopathy (DR) by using spectral-domain optical coherence tomography (SD-OCT) and optical coherence tomography angiography (OCT angiography).
We retrospectively studied patients with DR who presented CWSs and had been imaged by SD-OCT angiography. The retinal layer localisation and dimensions of the CWSs were assessed on SD-OCT, while the decorrelation signal generated by the CWSs and the vascular density (VD) of the superficial capillary plexus (SCP) and deep capillary plexus around the CWSs and in the macula were assessed on OCT angiography.
A total of 87 eyes of 57 DR patients were included. All CWSs were located in the retinal nerve fibre layer and exhibited a decorrelation signal on OCT angiography. In 68 eyes (78.1%), hyporeflective cavities appearing as cysts in the CWS were noted, especially when were peripheral and large (P < 0.0001). The thickness averaged 211.8 ± 80.02 mm and was positively influenced by recent diabetes history, glycaemic dysregulation, posterior pole localisation and a high VD of the SCP around the CWS, while the surface area averaged 0.33 ± 0.24 mm and was influenced only by a low VD of the SCP around the CWS (P < 0.001). In 72 eyes (82.7%), the non-perfused areas were predominant in the periphery of the CWS.
The features of CWSs are influenced by systemic factors, such as history and severity of diabetes, in association with local factors, such as localisation and retinal ischaemia. The peripheral localisation of ischaemia confirms the hypothesis that CWSs are sentinel lesions.

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