Retinal thickening refers to the thickness of the retina exceeding the normal value, the normal thickness of different parts of the retina is different for patients of different ages. When measuring the retinal thickness in OCT examination, the instrument will automatically retrieve the normal value of the corresponding parts for comparison, and any abnormality will be indicated by red color. Retinal thickening can be caused by a variety of reasons, the following are common: First, retinal edema, commonly found in patients with choroiditis, retinitis, retinal vein occlusion, diabetic retinopathy, retinal and choroidal blood vessels in the role of inflammation to increase the permeability, triggered by the leakage of intravascular fluid into the retinal tissue space, so that the thickness of the retina increased. Second, retinal split, that is, caused by the separation of the retinal neuroepithelial layers, most patients are caused by congenital developmental anomalies, and a small number of patients are complications caused by high myopia and trauma. Third, pre-retinal membrane, due to the formation of proliferative membrane in front of the retina, the formation of retinal pull can also lead to retinal thickening.