Identification of tear lipid biomarkers in women with dry eye disease and the impact of intense pulsed light therapy: a case-control study.

Background: The tear-film lipid layer (TFLL) constitutes the outermost barrier of the ocular surface, reducing evaporation and stabilising the tear film. In aqueous-deficient dry eye (ADDE) and Meibomian-gland dysfunction (MGD), compositional changes in the TFLL compromise this protective role. The present study was designed to characterise the tear-lipid fingerprints associated with ADDE and MGD, to compare them with those of healthy subjects, and to assess the impact of intense pulsed-light (IPL) therapy on the tear lipidome in MGD.

Methods: In a multicentre, prospective, observational-interventional case-control pilot study, 52 participants were enrolled in two phases: a discovery cohort (9 ADDE, 15 MGD, 13 controls) and an independent validation cohort (15 additional subjects). Tear lipids were profiled by ultra-high-performance liquid chromatography-mass spectrometry (UHPLC-MS). Unsupervised principal-component analysis (PCA) explored global variance; supervised partial least-squares discriminant analysis (PLS-DA) and orthogonal PLS-DA (OPLS-DA) defined group differences and yielded candidate biomarkers, with model robustness confirmed by permutation testing and CV-ANOVA. MGD participants received IPL at baseline, day 15, and day 45; clinical metrics and tear samples were obtained before and after therapy.

Results: A total of 176 lipid species were identified and quantified in positive- and negative-ion modes (ESI + and ESI-). Supervised PLS-DA clearly separated ADDE, MGD and control samples, while OPLS-DA highlighted 48 lipids that differed significantly among groups (p < 0.05). Both dry-eye subtypes were characterised by a pronounced depletion of lysophospholipids (LPE, LPC, LPG, LPI; fold change < 0.5) and an enrichment of (O-acyl)-ω-hydroxy fatty acids (OAHFA; fold change > 2) relative to controls. Cholesteryl esters (ChE) showed a subtype-specific elevation only in the MGD-versus-control comparison (fold change > 2). Permutation testing and CV-ANOVA confirmed the robustness of the ADDE-versus-MGD discrimination model. Although IPL therapy significantly improved clinical metrics such as tear break-up time and lissamine-green staining, the changes observed in the tear lipid profile were not statistically significant.

Conclusions: Dry-eye subtypes appear to possess discrete lipidomic signatures; consequently, the lipid panel identified here could serve as a set of potential therapeutic targets. The dissociation between clinical improvement and lipidomic stability after IPL indicates that the therapy may benefit the ocular surface through mechanisms other than large-scale remodelling of the tear-film lipid layer, highlighting the need to explore complementary therapeutic pathways.