Comparative Evaluation of Conjunctival Impression Cytology and Conventional Tear Film Tests in Diabetic Dry Eye Disease

Introduction: Dry eye disease (DED) in type 2 diabetes mellitus (T2DM) is common yet frequently underdiagnosed. Conventional tear film tests may not always correlate with ocular-surface pathology, particularly in diabetics with neurosensory dysfunction. This study evaluated the diagnostic performance of conjunctival impression cytology (CIC) compared with standard dry eye tests in T2DM. Methods: In this cross-sectional study, 200 patients with T2DM aged >45 years underwent a comprehensive ophthalmic evaluation. Dry eye assessment included ocular surface disease index (OSDI), tear break-up time (TBUT), Schirmer I and II, Rose Bengal staining, fluorescein clearance test (FCT), tear film height (TFH) and CIC graded according to Nelson’s classification. Sensitivity, specificity and exploratory receiver operating characteristic (ROC) curve analyses were performed relative to CIC-based classification. Associations with clinical variables were analysed. Results: The mean age was 56.8 ± 8.4 years. Prevalence of DED increased with longer duration ( p = 0.003) and severity of diabetic retinopathy (DR) ( p = 0.01), while age, gender and glycated haemoglobin (HbA1c) showed no significant associations. Relative to CIC-based classification, conventional tear film tests demonstrated variable sensitivity and specificity relative to conjunctival impression cytology findings. CIC identified ocular surface morphological changes including goblet-cell loss in some patients with borderline tear film parameters. Conclusion: CIC identified ocular surface morphological changes associated with diabetic DED that were not consistently reflected by conventional symptom-based and tear film tests in this cohort. The findings suggest that structural ocular-surface alterations may contribute importantly to diabetic DED in addition to tear film dysfunction. A multimodal diagnostic approach incorporating both structural and functional assessment tools may provide a more comprehensive evaluation of diabetic DED.