The effect of active smoking, passive smoking, and e-cigarettes on the tear film: An updated comprehensive review.

Active tobacco smoking, passive smoking, and e-cigarette smoking have been associated with different systemic and ocular diseases. The precorneal tear film plays an important role in eye health and its analysis can provide useful information on ocular status. This review investigates the effects of different types of smoking on the precorneal tear film, by analyzing the peer-reviewed literature on this topic. Specifically, tear evaporation rate, stability, volume, ferning, osmolarity, and physical composition (lipids and proteins) of tear film are detailed. Most of the reported works show that cigarette smoking reduces tear film stability and quality by affecting its components. This review highlights that smoking severely affects the tear film, but a single test is not sufficient to determine these effects because smoking can impact different parts of the eye.