To evaluate the clinical utility of optical coherence tomography (OCT) in the assessment of psoriatic nail disease, focusing on its ability to detect early structural changes, quantify lesion severity, and monitor treatment outcomes. Patients with psoriasis (PsO) or psoriatic arthritis (PsA) presenting with nail involvement were enrolled between May 2022 and September 2023. A swept-source OCT system ( \(1.3 \, \mu \text {m}\) , 5 mm depth) was used to image all fingernails. Cross-sectional nail structures were analyzed, and grayscale values were quantified to assess nail integrity. Paired-sample t-tests were applied to compare grayscale values before and after disease progression or treatment ( \(P < 0.05\) ). OCT imaging revealed structural abnormalities such as nail plate separation, thinning, depressions, and low-reflectivity regions that were not visible to the naked eye. During disease progression, grayscale values significantly decreased, reflecting loss of nail integrity. Following 4 months of treatment, grayscale values increased by 6–10 units, indicating recovery of nail structure. OCT provided objective measurements that correlated with clinical improvement and offered greater sensitivity than visual inspection. OCT is a non-invasive, high-resolution imaging technique that enables early detection and quantitative monitoring of psoriatic nail disease. Grayscale analysis provides an objective metric for evaluating disease severity and treatment response, supporting OCT as a valuable tool for diagnosis, follow-up, and clinical decision-making in PsO and PsA patients.
