The aim of the study was to retrospectively evaluate the changes of corneal transparency in diabetic patients across 3 different age groups. We enrolled 135 diabetes mellitus (DM) patients and 154 control subjects in this retrospective and nonrandomized study. Corneal backward light scattering information was collected from different corneal layers and annuli by using Scheimpflug tomography (Pentacam HR). The corneal densitometry analysis results varied between different age groups. In the 60 to 69 age group, the anterior layer at zone 0 to 2 mm had better corneal clarity in controls than in DM patients. Corneal densitometry values were markedly higher in diabetic eyes compared with control eyes in 70 to 79 age group when considered by central zones of total cornea at the 2 to 6 mm. The corneal transparency increased in 80 to 89 years DM patients in the majority of corneal zones. Besides, a weak correlation was found between the occurrence of DM and corneal densitometry at 0 to 2 mm and 2 to 6 mm concentric radial zones in anterior, posterior and total corneal depth. Diabetic patients showed higher values of corneal densitometry especially in central annuli in anterior layer than controls aged 60 years and over. Corneal transparency decreases differently in DM eyes across 3 age groups.