Purpose <p>To investigate the peripapillary (p) and subfoveal (sf) choroidal vascular index (CVI) parameters in newly diagnosed major depressive disorder (MDD).</p> Methods <p>This prospective comparative study was conducted on 50 patients with newly diagnosed MDD and 50 age- and sex-matched healthy participants. All participants underwent an ophthalmological examination, and their demographic characteristics were recorded. Choroidal images obtained from the HD-line optical coherence tomography sections of both groups were analyzed in both the foveal and peripapillary regions.Choroidal thickness measurements were obtained, and choroidal vascular parameters were determined using a specialized free software program.These parameters included the luminal choroidal area (LCA), stromal choroidal area (SCA), and total choroidal area (TCA).The ratio of LCA to TCA was defined as CVI.</p> Results <p>No statistically significant differences were found between the groups concerning choroidal thickness, optic disc head measurements, or peripapillary retinal nerve fiber layer thickness (p &gt; 0.05 for all).In the MDD group, the sfLCA was 0.11 ± 0.04 mm² and the pLCA was 0.12 ± 0.03 mm², whereas in the control group, these measurements were 0.16 ± 0.05 mm² and 0.16 ± 0.02 mm², respectively (p = 0.003 and p = 0.005,respectively).The sfCVI values were 0.61 ± 0.03 in the MDD group and 0.74 ± 0.03 in the control group, while the pCVI values were 0.64 ± 0.04 in the MDD group and 0.71 ± 0.03 in the control group (p &lt; 0.001).The TCA and SCA values were similar between the two groups (p &gt; 0.05 for both).</p> Conclusion <p>The findings highlight the significance of these current, non-invasive, rapid, and reproducible indices obtained through choroidal imaging for elucidating the etiopathogenesis and diagnosis of MDD,a disorder considered to have a neurodegenerative component.</p>