Cigarette smoking increases the harm of type 2 diabetes mellitus on corneal endothelial cell density (ECD), researchers found in a study published in Cornea.
While previous research has compared ECD and corneal morphology between patients with diabetes and healthy control individuals or between healthy smokers and nonsmokers, this is only the second study to investigate the impact smoking has on ECD and central corneal pachymetry (CCT) in patients with diabetes.
The investigators prospectively assessed 200 eyes of 200 patients (age range 50 to 70 years, 89 women). They recruited patients with diabetes from a retina specialist in a diabetes outpatient clinic. The other study participants had received eye exams at the general outpatient clinic. Smokers who participated in the study had smoked for at least 25 years. Patients with glaucoma, corneal diseases, systemic chronic conditions other than type 2 DM or hypertension, or history of intraocular surgery were excluded from the study.
Researchers conducted eye exams on all patients and fluorescein angiography and macular optical coherence tomography (OCT) on patients with DM, diagnosing patients with proliferative diabetic retinopathy (PDR), nonproliferative DR (NPDR), or no DR. They utilized a noncontact specular microscope to assess corneal ECD, morphology, and CCT.
Patients who smoked had significantly lower ECD compared with control individuals (P =.03 for patients without DM and P <.001 for patients with DM). Patients with diabetes who smoked had significantly thicker corneas compared with the control group individuals (P =.013).
Thirty-one (16 smokers 15 nonsmokers) of the 100 patients with DM had PDR and 54 had NPDR (25 smokers 29 nonsmokers).
“In our study, healthy smokers had a statistically significant lower ECD compared with the control group (P =.030), indicating that smoking alone decreased ECD by approximately 9%,” the researchers report. “The ECD of diabetic smokers was significantly lower than that of the control group (P =.001). The 15% reduction in ECD in diabetic smokers confirms that smoking exacerbates the deleterious effects of DM on the corneal endothelium. Our work brings a new discovery: ECD was significantly lower in healthy smokers than in diabetic nonsmokers (P =.012), implying that smoking has a more deleterious effect on ECD than diabetes alone.”
The researchers recommend ophthalmologists examine the ECD of any patient with DM who smokes prior to cataract surgery and protect corneal endothelial cells during phacoemulsification.
Limitations of the study included inability to determine exact time of onset of DM in many patients, that healthy control individuals and nondiabetic smokers did not undergo hyperglycemia or A1c testing.
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. Published online November 22, 2021. doi:10.1097/ICO.0000000000002917