**Background:** Meibomian gland dysfunction (MGD) is a leading cause of dry eye disease (DED), affecting hundreds of millions globally. While the tear film lipid layer is primarily affected, tear proteins are thought to play key roles in MGD etiology. Machine learning (ML) can identify patterns in complex proteomic data and highlight features important for disease classification. This study aimed to use ML to identify tear proteins associated with MGD severity, focusing on differences across severity levels rather than comparing healthy vs. diseased.
**Methods:** The dataset included 233 patients with MGD (levels 2-4) from the Norwegian Dry Eye Clinic (2017-2019). Tear samples were collected via Schirmer strips, and proteins were quantified using untargeted LC-MS and PEAKS X Pro software (FDR ≤1%, fold change ≥2, ANOVA). After preprocessing (removing contaminants, replacing missing values, log transformation, scaling), 2188 proteins were analyzed. An LGBMClassifier (boosting tree-based) was trained to predict MGD level (2, 3, or 4) from protein quantifications, with class imbalance handled via the 'is_unbalanced' parameter. Three additional binary models predicted each level vs. others. Model performance was evaluated on the training data using balanced accuracy, F1 score, and Matthews correlation coefficient (MCC). Feature importance was assessed using Shapley Additive Explanations (SHAP), with the top 15 proteins examined. A novel weighting technique adjusted SHAP values by model uncertainty (based on predicted probabilities). PEAKS X Pro identified proteins significantly different between MGD levels.
**Key Results:** The multiclass model achieved balanced accuracy 72%, F1 0.82, MCC 0.72. Binary models: MGD level 2 (balanced accuracy 95%, F1 0.80, MCC 0.78), level 3 (85%, 0.86, 0.69), level 4 (87%, 0.82, 0.73). Unweighted SHAP identified top proteins including S100-A8 (upregulated in DED), proline-rich protein 4 (PRP4, downregulated in DED), lysozyme C (downregulated in DED), polymeric immunoglobulin receptor, prostaglandin reductase 1, and immunoglobulins (IGKV2-24, IGLV8-61, IGLV6-57, IGA2, IGG1). Weighted SHAP added glutathione peroxidase 1, dynactin subunit 2, psoriasin, and ADH7 to the top 15 for the multiclass model. PEAKS analysis found 13 proteins significantly different between MGD levels, including thymidine phosphorylase; only mannose-1-phosphate guanyltransferase alpha overlapped with SHAP-identified proteins. S100-A8 showed statistically significant differences between MGD levels 2 and 3 (p<0.05) and borderline between levels 2 and 4 (p=0.052). PRP4 and lysozyme C showed trends but not significant.
**Clinical Implications:** The study demonstrates that ML combined with SHAP can identify tear proteins associated with MGD severity, many of which are known DED biomarkers (e.g., S100-A8, PRP4, lysozyme C) and others potentially novel (e.g., glutathione peroxidase 1, dynactin subunit 2). These proteins are involved in inflammation, immune response, oxidative stress, and normal ocular function, suggesting MGD is a complex condition with multiple pathways. The findings could lead to new biomarkers for MGD grading and potential therapeutic targets. However, the models were not externally validated, and the study did not include a healthy control group, limiting generalizability. Future work should validate these proteins in independent cohorts and explore their roles in MGD pathogenesis.