The effects of smoking on the tear film and on soft contact lenses.

Smoking is frequently associated with systemic and ocular diseases. Considering the fundamental role in eye health of the precorneal tear fluid, its analysis could offer unique contributions to gather information on the ocular status. Smoking has a negative effect on tear film stability and quality by affecting different components, which can be assessed only by multiple tests. In addition, smoking is a risk factor for microbial keratitis and corneal infiltrates in contact lens (CL) wearers. In this contribution, we analyzed the interaction between nicotine and CL materials. CLs from FDA groups I, II, IV, and V were incubated in a nicotine solution for $24 {h}$ and then in a saline solution for the next $24 {h}$. We monitored the amount of absorbed and released nicotine per CL by ultraviolet spectrophotometry, normalizing to the mass of the hydrated CL. Group IV and V CLs displayed the highest and lowest nicotine absorption, respectively. The results suggest that CL affinity for nicotine could be ascribed to the interaction between the positive charge of nicotine pyrrolidine nitrogen and the negative charges of the CLs.