ObjectiveTo observe the detrimental effect of airborne black carbon suspension solution of different concentrations on the tear film function of mice.

MethodsTwenty-eight SPF-grade male BALB/c mice, aged 6-8 weeks, were randomly divided into four groups, 0.5 mg/ml group, 1 mg/ml group, 5 mg/ml group, and control group, with 7 mice in each group.The right eyes of mice were dropped by 4 μl of 0.5 mg/ml, 1 mg/ml, 5 mg/ml black carbon suspension, or phosphate buffer solution, 3 times a day according to grouping.Tear volume, tear break-up time (TBUT), corneal fluorescein staining (CFS), and conjunctival congestion were assessed before treatment and 4, 7, 10, and 14 days after treatment.The use and care of experimental animals complied with the Regulations for Administration of Laboratory Animals in Peking Union Medical College Hospital (No.XHDW-2022-053).

ResultsAt 14 days after treatment, the tear volumes of 0.5 mg/ml group, 1 mg/ml group, 5 mg/ml group and control group were (2.74±0.74), (2.73±0.76), (2.31±0.67), and (5.31±0.36)mm, respectively.TBUT of the four groups were (4.87±0.28), (4.00±0.76), (3.23±0.43), and (6.22±0.22)seconds, respectively.CFS of the four groups were 4(3, 4), 5(5, 6), 7(7, 8) and 0(0, 1) points, respectively.Conjunctival congestion grades of the four groups were 2(2, 3), 2(2, 3), 3(2, 3) and 0(0, 1), respectively.There were statistically significant differences in tear volume among the four groups at different time points ( F _group=83.325, P<0.001; F _time=86.551, P<0.001; F _interaction=5.181, P<0.001). Before and at each time point after treatment, tear volumes were significantly lower in 0.5 mg/ml group, 1 mg/ml group, and 5 mg/ml group than in control group, and tear volumes in 0.5 mg/ml group, 1 mg/ml group, and 5 mg/ml group were significantly lower at 4, 7, 10, and 14 days after treatment than before treatment (all at P<0.05). There were statistically significant differences in TBUT among the four groups at different time points ( F _group=75.130, P<0.001; F _time=56.265, P<0.001; F _interaction=6.103, P<0.001). Before and at each time point after treatment, TBUT was significantly shorter in 0.5 mg/ml group, 1 mg/ml group, and 5 mg/ml group than in control group, and the TBUT was significantly shorter in 0.5 mg/ml group, 1 mg/ml group, and 5 mg/ml group at 4, 7, 10, and 14 days after treatment than before treatment, shorter in 1 mg/ml group and 5 mg/ml group at 14 days after treatment than 4, 7 and 10 days after treatment (all at P<0.05). There were statistically significant differences in CFS score and conjunctival congestion grades among the four groups at different time points, but the interactions between concentration group and measurement time were not statistically significant (CFS: H _group=59.249, P<0.001; H _time=49.959, P<0.001; H _interaction=15.980, P=0.192.conjunctival congestion grade: H _group=57.622, P<0.001; H _time=42.062, P<0.001; H _interaction=12.565, P=0.401). Before and at each time point after treatment, the CFS scores and conjunctival congestion grades were significantly higher in 0.5 mg/ml group, 1 mg/ml group, and 5 mg/ml group than in control group, and CFS scores and conjunctival congestion grades were significantly higher in 0.5 mg/ml group, 1 mg/ml group, and 5 mg/ml group at 4, 7, 10, and 14 days after treatment than before treatment (all at P<0.05).

ConclusionsThe exposure of airborne black carbon on the ocular surface causes damage to tear film function and ocular surface inflammation in BALB/c mice.Within a certain concentration and time range, the tear secretion decreases, TBUT shortens, CFS and conjunctival congestion increase.