Distinct Tear Element Signatures in Primary Acquired Nasolacrimal Duct Obstruction Identified by Particle-Induced X-Ray Emission

Purpose: To investigate the etiology of primary acquired nasolacrimal duct obstruction (PANDO) by characterizing the elemental composition of tear and blood samples from affected patients. Methods: Tear samples were prospectively collected from each eye of adults with PANDO and matched controls using Schirmer strips. Fingertip blood was obtained using the same absorbent material. Samples were analyzed with particle-induced x-ray emission (PIXE) to quantify multi-element profiles. Statistical analysis included paired testing for intraindividual comparisons in unilateral PANDO, independent-group comparisons between PANDO and controls, and multivariate methods to assess overall group separation. Results: Participants included 15 patients with PANDO and 15 controls (14 females each), with mean ages of 57.29 ± 15.35 and 53.27 ± 14.89 years, respectively. Twelve elements were detected in tears and 11 in blood. Compared with controls, the PANDO group had significantly (P < 0.05) higher tear levels of sodium (Na) and chlorine (Cl) in both affected and unaffected eyes, and higher phosphorus (P) and sulfur (S) levels in unaffected eyes. There were no significant differences between affected and unaffected eyes in unilateral PANDO. In blood, only copper (Cu) differed significantly between groups. Multivariate analyses demonstrated clear group separation in tears but not blood profiles. Conclusions: Patients with PANDO have a distinct tear elemental signature characterized by high Na levels. Our findings suggest that bilateral biochemical alterations may precede clinically detectable obstruction and that PANDO is a product of local ocular processes rather than systemic influences. Tear elemental analysis is a promising noninvasive approach for detecting early or subclinical changes in PANDO and improving understanding of its pathophysiology.