Background: Diabetic eye surface disease, including dry eye syndrome, corneal neuropathy, and diabetic retinopathy, is a common complication of diabetes. Tear fluid biomarkers may aid in early diagnosis and disease monitoring. The objective of this systematic review was to identify and evaluate tear fluid biomarkers in diabetic ocular surface disease according to PRISMA guidelines. Methods: PubMed, Scopus, and Embase databases were searched through June 2025. Eligible studies included clinical and observational studies measuring proteins, lipids, cytokines, trace elements, or nucleic acids in tear fluids in patients with diabetes. Results: The search identified 198 studies, and of those, 30 studies were included, comprising 14 original investigations with 871 participants (133 with type 1 diabetes, 453 with type 2 diabetes, 16 with pre-diabetes, and 269 healthy controls). The main biomarker categories were cytokines (IL-6, IL-8, TNF-α, and MMP-9), neuropeptides (substance P, NPY), proteins (IGFBP-3, progranulin), lipids, glycans, microRNAs, circRNAs, and trace elements. Conclusions: More than a dozen biomarkers in the tear fluid have been identified that may reflect diabetes-related changes in the ocular surface. Tear fluid analysis may be a valuable tool in personalizing the diagnosis and treatment of diabetic ocular surface diseases, but further studies are needed to confirm its clinical significance.

To evaluate the impact of keratoconus on visual quality and quality of life among Polish patients by integrating subjective assessments using the Keratoconus Outcomes Research Questionnaire (KORQ) with objective clinical measurements. A total of 100 patients (80% men, 20% women; median age: 39 years) with clinically diagnosed keratoconus completed the locally validated Polish version of the KORQ, including two subscales: Activity Limitation (18 items) and Symptoms (9 items). Objective data collected included best-corrected visual acuity (BCVA), corneal topography, pachymetry, and higher-order aberrations (HOA). Statistical analyses included biweight midcorrelations and robust linear regression models adjusted for age and gender. The mean Activity Limitation score was 51.53 (SD = 17.19) and the Symptoms score was 55.60 (SD = 16.14), indicating moderate functional impairment and symptom burden. The most challenging activities were night driving (mean = 2.06), seeing small distant objects (mean = 2.09), and coping with poor lighting (mean = 2.05). The most bothersome symptoms were distorted vision (mean = 1.84), sensitivity to smoke (mean = 2.05), and dusty environments (mean = 2.01). Higher-order aberrations, especially in the worse-seeing eye, showed the strongest associations with KORQ scores across both subscales (e.g., for Symptom subscale: HOA: β = 2.84; p = 0.004; vertical coma: β = 5.83; p = 0.019), while BCVA in the better-seeing eye was significantly associated with both lower symptom burden (β = -9.83; p = 0.047) and functional limitation (β = -12.13; p = 0.042). Traditional structural parameters, such as Kmax and corneal thickness, showed no significant predictive value. Keratoconus significantly impairs visual functioning and causes a high symptom burden among Polish patients. Best-corrected visual acuity and higher-order aberrations, especially in the worse-seeing eye, are the strongest predictors of reduced vision-related quality of life. These findings emphasize the need to focus clinical management on improving optical quality, rather than solely correcting structural corneal features.