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Diabetes mellitus (DM) affects corneal biomechanical parameters. We compared analyses using ORA (Ocular response analyser) and Corvis ST to determine the influence of disease duration, hyperglycaemia and haemoglobin A1c (HbA1c) levels on these parameters.This observational, cross-sectional, observer-masked study assessed one eye of 94 consecutive DM patients and 41 healthy subjects. Two DM groups were analysed: the uncontrolled DM group (n= 54) (HbA1c ≥ 7%) and the controlled DM group (n= 40) (HbA1c < 7%). Central corneal thickness (CCT) was measured by ultrasonic pachymetry and intraocular pressure (IOP) by Goldmann applanation tonometry. ORA and Corvis ST analyses were performed to evaluate the changes.Most of the Corvis ST parameters [Deformation amplitude (DA), A1 and A2 times, A1 velocity] in the uncontrolled DM group eyes were found to be significantly different to controls and controlled DM group eyes (p = 0.005, p = 0.001, p < 0.0001, p = 0.002, respectively). DA on the Corvis ST was correlated with blood glucose concentration (p = 0.004) and HbA1c percentage (p = 0.002). ORA corneal hysteresis was significantly lower in diabetic patients with elevated HbA1c than in control subjects (p = 0.001) and was affected by disease duration (p = 0.037), whereas the corneal resistance factor remained unaltered.A poor glucose control in DM affects corneal biomechanics measured by ORA and Corvis ST, which may cause high IOP measurements independent of CCT. The measurement of the corneal biomechanics should be taken into consideration in the clinical practice.