AIM: To evaluate alterations in conjunctival vascular density (CVD) and macular capillary density (MCD) in female patients with type 2 diabetes mellitus (T2DM) and gestational diabetes mellitus (GDM) using optical coherence tomography angiography (OCTA). METHODS: A total of 60 female participants were recruited, comprising 20 patients with T2DM, 20 patients with GDM, and 20 healthy age-matched controls (HCs). OCTA was used to assess superficial and deep retinal and conjunctival capillary plexuses. Subsequently, changes in MCD were analyzed using a circular segmentation method (C1-C6), a hemispheric quadrant segmentation method [superior right (SR), superior left (SL), inferior left (IL), and inferior right (IR)], and the early treatment diabetic retinopathy study (ETDRS) segmentation method (S, I, R, L). RESULTS: OCTA unequivocally demonstrated that the variations in CVD among HCs, T2DM, and GDM groups were statistically significant (P<0.001). In the superficial retinal capillary plexus (sRCP), significant differences were observed in the densities of total microvascular (TMI), microvasculature (MIR), and macrovascular (MAR) between patients with T2DM and HCs (P<0.05). Furthermore, the GDM group exhibited a more substantial reduction in MIR density compared to the T2DM group (P<0.01). In the deep retinal capillary plexus (dRCP), significant differences in the densities of TMI and MIR were identified between the T2DM group and HCs (P<0.05), with a notable difference in TMI density also observed between the GDM and T2DM groups (P<0.01). In the receiver operating characteristic (ROC) curve analysis, the area under the ROC curve (AUC) for TMI in sRCP between the T2DM group and HCs was 0.975, with a 95% confidence interval (CI) of 0.941–1. The AUC for MIR was highest in dRCP, with an AUC value of 0.914 and a 95%CI ranging from 0.847 to 0.981. In comparing the GDM and T2DM groups, the AUC for I region was maximized in sRCP, achieving a value of 0.978 with a 95%CI of 0.953–1. Additionally, the AUC for R region was maximized in dRCP, reaching a value of 0.99 with a 95%CI of 0.975 to 1. CONCLUSION: The sRCP and dRCP densities show higher diagnostic sensitivity for T2DM and GDM. OCTA holds potential as a significant instrument for the early diagnosis and differentiation of T2DM and GDM.