Abstract
INTRODUCTION: Reduced corneal sensation in individuals with type 2 diabetes mellitus (T2DM) leads to a dissociation between dry eye disease (DED) signs and symptoms, thereby affecting diagnostic accuracy. This study aimed to investigate the correlation between ocular surface signs and diabetic peripheral neuropathy (DPN) symptoms in patients with T2DM-associated DED. METHODS: The Michigan Neuropathy Screening Instrument Questionnaire (MNSIQ) was used to categorize patients with T2DM into MNSIQ-DPN and non-DPN groups. Ocular irritation symptoms were evaluated using the Ocular Surface Disease Index (OSDI) questionnaire. Ocular surface lesions were assessed via Cochet-Bonnet esthesiometry, corneal fluorescein staining (CFS), the Schirmer I tear test (SIT), tear meniscus height (TMH), noninvasive keratography break-up time (NIKf-BUT), and the meibomian gland loss (MGL) grade detected by OCULUS. Corneal nerve fiber parameters were evaluated using in vivo confocal microscopy (IVCM). RESULTS: A total of 116 patients with T2DM, comprising 76 non-DPN patients and 40 MNSIQ-DPN patients, along with 51 age-matched participants without diabetes, were enrolled. Although OSDI scores were equivalent between MNSIQ-DPN patients and non-DPN patients, MNSIQ-DPN patients presented significantly more severe CFS (p < 0.001), meibomian gland dysfunction (MGD) (p < 0.001), corneal nerve fiber loss (p < 0.001), sensory dysfunction (p = 0.02), and corneal microneuromas (p < 0.001). The MNSIQ score was significantly positively correlated with CFS (p < 0.001); MGD (p < 0.01); corneal nerve fiber loss, including corneal nerve fiber density and length and branch density, in the paracentral (all p < 0.001) and inferior-whorl areas (p < 0.01, p < 0.05 and p < 0.01, respectively); and corneal microneuromas, characterized by increased microneuroma numbers (p < 0.001) and areas (p < 0.001) in these regions. CONCLUSION: MNSIQ scores were significantly and robustly correlated with the presence of corneal epithelial defects, MGD, and nerve fiber loss in patients with T2DM. These findings suggest that DPN is a critical factor in diabetic ocular surface complications, highlighting the importance of the MNSIQ for assessing these conditions.