Total corneal astigmatism magnitude and vector orientation in diabetic and non-diabetic Malay eyes

The influence of diabetes mellitus (DM) on total corneal astigmatism (TCA) remains incompletely understood. Using total keratometry (TK), this study characterised TCA magnitude and orientation in a Malay adult population and evaluated the influence of metabolic control and ocular parameters on TCA.

This cross-sectional study analysed 190 eyes (88 non-diabetic; 102 diabetic). TCA magnitude and axis were derived from TK obtained using swept-source optical coherence tomography (IOLMaster 700, Carl Zeiss Meditec, Germany) and decomposed into power-vector components; J0 (horizontal/vertical) and J45 (oblique). Corneal endothelial parameters were measured using specular microscopy (Topcon SP-1P, Japan). Group comparisons were performed using Welch's t-test. Within diabetic eyes, linear regression models identified independent predictors of TCA magnitude and orientation, adjusting for age, glycated haemoglobin (HbA1c), DM duration, cumulative metformin exposure, central corneal thickness, endothelial cell density, and white-to-white diameter.

TCA magnitude did not differ significantly between diabetic and non-diabetic eyes (p = 0.066). Vector analysis demonstrated no significant between-group difference in J0 or J45, with substantial vector centroid overlap. In diabetic eyes, higher HbA1c was independently associated with greater TCA magnitude, while increasing age was independently associated with a shift towards more negative J0 values. DM duration and metformin exposure were not independently associated with TCA magnitude or vector components.

Diabetes status alone was not associated with systematic differences in TCA magnitude or orientation. Age and metabolic control were the strongest factors associated with TCA characteristics. Vector-based analysis provides a robust framework for astigmatism assessment in diabetic and non-diabetic eyes.