Association of the glucose metabolism continuum (fasting plasma glucose/HbA1c) with tear-film stability and secretion: ocular surface evidence across non-diabetes, prediabetes, and diabetes

Background Whether gradations in glycemia across non-diabetes, prediabetes, and diabetes relate to tear−film homeostasis and dry eye disease (DED) remains uncertain, and explicitgraded association evidence is limited. Methods In a single−center cross−sectional study (April 2024–March 2025), we enrolled 300 adults by quota ( n = 100 per stratum). Same−day hemoglobin A1c (HbA1c) and fasting plasma glucose (FPG) classified strata and were also modeled continuously. Co−primary outcomes were non-invasive tear break−up time (NIBUT) and Schirmer I (no anesthesia). Secondary outcomes included fluorescein tear break-up time (TBUT), ocular surface disease index (OSDI), National Eye Institute (NEI) staining, meiboscore, tear meniscus height, bulbar redness, tear osmolarity, and matrix metalloproteinase-9 (MMP−9). DED was defined as OSDI ≥13 plus ≥1 sign [NIBUT