ObjectiveTo investigate the change of subfoveal choroidal thickness (SFCT) and the relationship between SFCT and the severity of the diabetic retinopathy using enhanced depth imaging optical coherence tomography (EDI-OCT). MethodsA total of 164 eyes (93 patients) of type 2 diabetes mellitus (DM) were included in this study. The patients included 34 males and 59 females, with an average age of (59.3±5.6) years, with an average diabetes duration of (5.11±4.64) years. The patients were divided into 4 groups according to international classification standards of DR, including non-diabetic retinopathy (NDR) group (64 eyes), mild non-proliferative diabetic retinopathy (NPDR) group (33 eyes), moderate NPDR group (37 eyes), and severe NPDR group (30 eyes). The control group included 25 normal subjects (42 eyes). All patients underwent visual acuity, intraocular pressure, slit lamp microscope, indirect ophthalmoscope, A/B-type ultrasound scan, frequency domain optical coherence tomography (SD-OCT) examination, as well as fasting blood glucose and mean arterial blood pressure measurement. The mean axial length was (23.04±0.78) mm, mean fasting blood glucose was (8.88±2.59) mmol/L, mean arterial pressure was (100.44±9.63) mmHg. SFCT of all eyes were measured by EDI-OCT. The relationship between SFCT and the severity of the diabetic retinopathy, DM duration, fasting blood glucose, the mean arterial pressure, axial length was analyzed by one-way ANOVA. ResultsThe mean SFCT was (224.24±42.10) μm in DM group and (276.77±48.07) μm in normal control group, the difference was statistically significant (F=23.86, P < 0.05). The mean SFCT was also statistically significant between all DM groups (P < 0.05). There were negative linear correlation between SFCT of all patients and the severity of retinal lesions (r=-0.555, P=0.000), and between SFCT and DM duration (r=-0.332, P < 0.05). But SFCT was independent of fasting plasma glucose (r=-0.123, P > 0.05), mean arterial pressure (r=-0.116, P > 0.05), and axial length (r=-0.018, P > 0.05). ConclusionsSFCT in DM eyes is thinner than that in normal controls. SFCT is different in the NDR, mild NPDR, moderate NPDR, severe NPDR patient. Severe DR patients have much thinner SFCT.