The coexistence of diabetes and smoking leads to a significant decrease in ECD. Photo: Francis W. Price Jr., MD.
The coexistence of diabetes and smoking leads to a significant decrease in ECD. Photo: Francis W. Price Jr., MD. Click image to enlarge.

Despite known diabetes-related corneal endothelial changes and effects of smoking on corneal endothelial cells, only one study has investigated the coexistence of both on corneal cell characteristics. The researchers evaluated which of the two is more harmful to corneal morphological parameters and corneal endothelial cell density (ECD).

A total of 200 patients between the ages of 50 and 70 were assigned to four groups: smokers with type 2 DM, nonsmokers with type 2 DM, healthy smokers and healthy nonsmokers (control group). Non-contact specular microscopy was used to measure ECD, coefficient of variation of cell area, percentage of hexagonal cells and central corneal pachymetry (CCT).

Results showed that healthy smokers had a statistically significant lower ECD compared with controls, indicating that smoking alone can decrease ECD by approximately 9%. The ECD of diabetic smokers was significantly lower than that of the control group.

“The 15% reduction in ECD in diabetic smokers confirms that smoking exacerbates the deleterious effects of DM on the corneal endothelium,” the authors concluded. “Our work brings a new discovery: ECD was significantly lower in healthy smokers than in diabetic nonsmokers, implying that smoking has a more deleterious effect on ECD than diabetes alone.”

The only other previous study that looked into this association reported a decrease in ECD in diabetic smokers compared with healthy nonsmokers and an increase in CCT in diabetic nonsmokers compared with healthy smokers. In this current study, CCT was thicker in diabetic smokers compared with controls.

This study also confirmed that in addition to the retina, it is necessary to include the cornea when diagnosing DM.

“In diabetics, awareness of multiorgan toxicity follows the diagnosis of DM, whereas this awareness occurs much later in smokers,” the study authors explained. “A smoker can stop the toxic effects immediately (if he is able to do so, as it is a chemical dependency), but a diabetic cannot simply eliminate diabetes by his own decision. Our study confirms that the coexistence of DM and smoking leads to a significant decrease in ECD and is responsible for thicker corneas. Cigarette smoking is more harmful to corneal endothelial cells than DM alone.”

Anticić-Eichwalder M, Lex S, Sarny S, et al. Effects of type 2 diabetes mellitus and smoking on changes in corneal endothelial morphology and cell density. Cornea. 2021;00:1-5.