**Background:** Type 1 diabetes mellitus (T1DM) is a chronic autoimmune disease that can affect all ocular structures, including the tear film and meibomian glands. Dry eye disease (DED) is common in diabetes, but most studies focus on type 2 diabetes or pediatric T1DM. This study aimed to objectively assess tear film layers and meibomian glands in adults with T1DM without retinopathy using a noninvasive ocular surface analyzer (OSA), and to compare results with healthy controls.
**Methods:** A cross-sectional case-control study was conducted at the University of Seville (Spain) from January to May 2022. Eighty-eight participants were enrolled: 44 with T1DM (diagnosed ≥3 years, no retinopathy on fundus imaging) and 44 age- and sex-matched controls (HbA1c ≤5.6%). Exclusion criteria included ocular infection/inflammation, use of topical or systemic medications affecting the tear film, pregnancy, contact lens wear, and use of lubricants within 1 week. All participants underwent noninvasive assessment with the ICP Ocular Surface Analyzer (SBM System) measuring: limbal and bulbar redness (Efron scale), lipid layer thickness (LLT, Guillon classification), tear meniscus height (TMH), first and mean noninvasive tear break-up time (FNIBUT, MNIBUT), and meibomian gland loss (MGL) percentage in upper and lower eyelids (Meiboscale). Invasive tests included Schirmer I test (SIT) and fluorescein tear break-up time (TFBUT). Subjective symptoms were assessed using OSDI and SPEED questionnaires. HbA1c was measured in all participants. Statistical analysis used independent t-test or Mann-Whitney U test for continuous variables, chi-square for categorical, and Pearson/Spearman correlations. Sample size was calculated based on TMH (minimum 31 per group).
**Key Results:** The T1DM and control groups were similar in age (mean 31.00 vs. 30.09 years), sex, and visual acuity. HbA1c was significantly higher in T1DM (6.88% vs. 4.99%, p<0.001). No significant differences were found in OSDI (median 12.50 vs. 8.33, p=0.637) or SPEED scores (median 4.00 vs. 4.00, p=0.563). Noninvasive tests showed: limbal/bulbar redness higher in T1DM (median grade 2 vs. 1, p=0.010); LLT lower in T1DM (median Guillon pattern 1 vs. 2, p<0.001); TMH lower in T1DM (median 0.20 mm vs. 0.29 mm, p<0.001); FNIBUT lower in T1DM (median 4.41 s vs. 5.14 s, p<0.001); MNIBUT lower in T1DM (median 8.65 s vs. 9.80 s, p<0.001). MGL in the lower eyelid was significantly higher in T1DM (median 36.00% vs. 22.00%, p<0.001); upper eyelid MGL was not significantly different (median 22.50% vs. 19.00%, p=0.097). Invasive tests: SIT lower in T1DM (median 5.00 mm vs. 5.50 mm, p=0.001); TFBUT lower in T1DM (median 13.00 s vs. 21.5 s, p<0.001). Correlation analyses showed HbA1c was inversely correlated with TMH (ρ=-0.584, p<0.001), LLT (ρ=-0.361, p=0.001), FNIBUT (ρ=-0.525, p<0.001), MNIBUT (ρ=-0.399, p<0.001), SIT (ρ=-0.317, p=0.003), and TFBUT (ρ=-0.566, p<0.001), and directly correlated with limbal/bulbar redness (ρ=0.226, p=0.034) and lower eyelid MGL (r=0.396, p<0.001). In the T1DM group, diabetes duration was inversely correlated with LLT (ρ=-0.400, p=0.007) and directly correlated with upper eyelid MGL (ρ=0.413, p=0.005).
**Clinical Implications:** This study demonstrates that adults with T1DM without retinopathy have significant objective signs of dry eye disease, including reduced tear film stability, decreased lipid and aqueous layers, and increased meibomian gland loss, particularly in the lower eyelid. Importantly, subjective symptom questionnaires (OSDI, SPEED) did not differ between groups, suggesting that T1DM patients may be asymptomatic due to possible corneal neuropathy. Therefore, dry eye cannot be ruled out by symptoms alone; regular anterior segment examinations using noninvasive tools like the OSA are recommended for early detection and management. The correlations with HbA1c and diabetes duration highlight the importance of glycemic control in preserving ocular surface health. Limitations include the cross-sectional design, relatively small sample size, and lack of masking. Future longitudinal studies are needed to confirm causality.