Smoking negatively impacts ocular surface health and corneal nerve metrics.

Abstract

Purpose: To evaluate the effects of smoking on ocular surface through comprehensive analysis of corneal nerves, corneal epithelium, dendritic cells (DCs), and clinical assessments.

Methods: This cross-sectional study included 250 healthy smokers and 272 healthy non-smokers. Patients' smoking status and duration were recorded. In vivo confocal microscopy was performed to assess 7 quantitative corneal nerves parameters, 3 corneal neuroma parameters, 3 DCs parameters, and 3 epithelial parameters. Ocular surface evaluations included tear break-up time (TBUT), ocular surface and corneal staining, corneal sensitivity, and Schirmer test. Ocular Surface Disease Index questionnaire was used for symptom assessment.

Results: Compared to non-smokers, smokers exhibited significantly lower corneal nerve fiber density (CNFD), nerve branch density, nerve fiber length, nerve total branch density, corneal nerve fiber area (CNFA), and corneal nerve fractal dimension (CFracDim; all p<0.001). Smokers also presented with a significantly swollen corneal nerve fiber (p<0.001). Longer smoking duration was significantly associated with lower CNFD (β=-0.04, P=0.010), lower CNFA (β=-0.00002, P=0.033), and lower CFracDim (β=-0.0008, P=0.016). Additionally, a significantly larger neuroma total area (p=0.040), size (p<0.001) and perimeter (p<0.001), as well as a significantly higher DCs density (p<0.001), DCs count (p=0.003), and lower DCs elongation which suggested higher DCs maturity (p<0.001), were observed in the smoking group. Smokers demonstrated significantly higher ocular surface staining scores (p<0.001) and reduced TBUT (p=0.001). Corneal epithelial circularity was borderline higher in the smoking subjects (p=0.059).

Conclusions: Smoking is associated with significant alterations in corneal nerve morphology and quantity, increased immunological cells, and compromised ocular surface integrity.