Abstract
Objective
To analyse age-related changes in differential corneal thickness (DCT) and curvature (DCC) between the two principal meridians and between the vertical and horizontal meridians, and to examine their relationship with with-the-rule (WTR) and against-the-rule (ATR) astigmatism.Methods
This retrospective study included 400 patients (100 per age group: 6-20, 21-40, 41-60 and ≥61 years). The left eye was analysed for each participant. Corneal thickness (CT) and curvature (CC) were measured within the central 3 mm zone along the two principal, vertical and horizontal meridians. The mean differential thickness (DCT1) and curvature (DCC1) between the two principal meridians, as well as the mean differential thickness (DCT2) and curvature (DCC2) between the vertical and horizontal meridians were calculated and compared across age groups. To account for axis orientation, power vector transformation was applied to DCC1, decomposing it into DCC10 (WTR/ATR component) and DCC145 (oblique component). Subgroup analyses restricted to WTR astigmatism were performed to control for axis orientation in the thickness analysis.Results
DCT1 decreased with age but showed no significant change in the WTR subgroup (p = 0.14), indicating the apparent decline was driven by age-related shifts in axis composition. DCT2 remained stable across age groups (p = 0.19). DCC10 decreased significantly with age, from -2.09 to -0.08 D (p 45 did not change significantly (p = 0.30). DCC2 also decreased significantly with age (p 0.05).Conclusions
After controlling for axis orientation in the WTR subgroup, DCT1 and DCT2 did not vary with age. The significant age-related decreases in DCC10 and DCC2 confirm that anterior CC changes are the primary drivers of the WTR-to-ATR astigmatic shift. These age-related changes were consistent between sexes.