Purpose: To compare 5-year changes of central and peripheral corneal thickness, corneal volume, and keratometry between diabetic and non-diabetic individuals (>40 years) in a population-based study.

Materials and methods: Right eye corneal indices of the 333 diabetic persons were compared with 2865 non-diabetics. Studied indices included the apical corneal thickness (ACT), minimal corneal thickness (MCT), thickness values on corneal rings of 4 mm, 6 mm, and 8 mm in diameter, the volume of the 10 mm of the corneal diameter, and the central 3 mm keratometry in two steep (Kmax) and flat (Kmin) axes as measured with Pentacam (Oculus, Inc, Lynnwood, WA).

Results: In the diabetic and non-diabetic groups, respectively, the 5-year change was +0.1 ± 11.9 and -1.2 ± 11.9 μm (p = 0.035) for ACT, -1.1 ± 12.1 and -2.4 ± 11.9 μm (p = 0.056) for MCT, -3.9 ± 12.6 and -5.1 ± 12.3 μm (p = 0.007) for the 4 mm ring, -5.0 ± 15.3 and -7.5 ± 14.5 μm (p = 0.006) for the 6 mm ring, and -7.0 ± 20.1 and -10.8 ± 19.2 μm (p = 0.011) for the 8 mm ring. The diabetic group showed less reduction in corneal volume (-0.5 ± 1.8 mm³) compared to non-diabetics (-0.8 ± 1.6 mm³) (p = 0.030). Kmax (+0.3 ± 0.5D vs. +0.4 ± 0.5, p = 0.028) and Kmin (+0.4 ± 0.5D vs. +0.5 ± 0.5, p = 0.005) showed less change in diabetics compared to non-diabetics.

Conclusions: The overall patterns of change in corneal thickness and shape in over 40-year old diabetics are similar to non-diabetics, such that with aging, reduced thickness and increased keratometry take the cornea towards a prolate shape. However, the age-related changes in central and peripheral corneal thickness, volume and corneal shape are less pronounced in diabetic subjects.