Smoking negatively impacts ocular surface health and corneal nerve metrics

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

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.

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).

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