<p>Obsessive-compulsive disorder (OCD) is a prevalent neurological condition characterized by recurring obsessive thoughts and compulsive behaviors. The underlying mechanisms of the disorder remain poorly understood due to its considerable heterogeneity. Given the extensive brain impairments observed in OCD, this study aimed to investigate gray matter volume and functional connectivity in individuals with OCD using a multimodal neuroimaging approach, while also exploring the relationship between these neural changes and clinical symptom severity. Structural and resting-state functional magnetic resonance imaging data were collected from 56 OCD patients and 41 healthy controls. Voxel-based morphometry analysis was employed to identify gray matter volume differences between the patient and control groups. Compared to healthy controls, patients exhibited reduced gray matter volume in visual processing regions, including the cuneus, left calcarine, and middle occipital gyrus. Furthermore, whole-brain functional connectivity analysis was conducted on these regions with abnormal gray matter volume, showing increased connectivity between the visual processing areas and subcortical and prefrontal regions. Additionally, gray matter volume reductions in the left calcarine and middle temporal gyrus were significantly correlated with higher scores on the Yale-Brown Obsessive Compulsive Scale, suggesting a link between visual processing abnormalities and the severity of clinical symptoms. These findings highlight structural and functional alterations in visual-related brain regions as key contributors to the pathophysiology of OCD, providing valuable insights into its neural basis and potential avenues for therapeutic intervention.</p>