Atmospheric pollutant black carbon induces ocular surface damage in mice

The threats of air pollution to human health have been gradually discovered, including its effects on eyes. The purpose of the study is to investigate the potential correlation between ocular surface exposure to black carbon and ocular surface structural damage as well as tear film dysfunction. To achieve this goal, 60 6-8-week-aged male BALB/C mice were randomly divided into 4 groups (n = 15). 0.5 mg/ml (group A), 1 mg/ml (group B), 5 mg/ml (group C) black carbon suspension droplets and PBS solution (group D) were used in the right eyes, 4 μl per time of three times per day. Tear break-up time, corneal fluorescein staining scores, and tear volume were assessed before treatment (day 0) and on days 4, 7, 10, and 14 after treatment. On day 14, the mice were sacrificed, and corneal and conjunctival tissues were collected for histological analysis. As the exposure time increased, there were no significant changes in the measured parameters from PBS-treated group of mice (P > 0.05). However, in the black carbon-treated group, there were significant decreases in tear film break-up time, significant increases in corneal fluorescein staining scores, and significant reductions in tear secretion (all P < 0.05). After 14 days, H&E staining of the corneal epithelium showed that in the PBS-treated group of mice, the corneal epithelial cells were neatly arranged, with no inflammatory cell infiltration, while in the black carbon-treated group, the corneal epithelium was significantly thickened, the basal cell arrangement was disrupted, the number of cell layers increased, and there was evidence of inflammatory cell infiltration. In the ultrastructure of the corneal epithelium, it could be observed that the black carbon-treated group had an increased amount of corneal epithelial cell detachment compared to the PBS-treated group, at the same time, the intercellular connections were looser, and there was a decrease in the number of microvilli and desmosomes in the black carbon-treated group. The results indicate that the ocular surface exposure to black carbon can result in a decrease in tear film stability and tear secretion in mice. Moreover, it can induce alterations in the corneal structure.