Fig. 1.

Overview of the experimental groups. a C-cigarette exposure groups contain medium- and long-term subgroups and the corresponding control mice. b E-cigarette exposure groups contain short-, medium-, and long-term subgroups, wherein nicotine-free E-cigarette and nicotine-containing E-cigarette were used with the exception of the long-term subgroup, in which only nicotine-containing E-cigarettes was used. The number of eyes per group is listed in the grey box below each group