Cigarette Smoking Deteriorates Dry Eye Parameters

Smokers have less tear meniscus height (TMH), mean Schirmer’s scores, and tear breakup time (TBUT), according to research results published in Indian Journal of Ophthalmology. 

While tobacco smoke is a known eye irritant that worsens dry eye, there is limited research on the effects of smoke on the eye. To further investigate, researchers compared the eyes of 40 patients (38 men, P <.001) who had smoked for at least 1 year and were active smokers with 40 age-matched patients who had no history of passive smoking. 

They classified smokers as light smokers (less than 20 cigarettes per day) or heavy smokers (more than 20 cigarettes in a day, n=4). They excluded patients with contact lenses or history of ocular surgery.

Patients described their past week experience using the Ocular Surface Disease Index (OSDI). Investigators measured the patients’ best-corrected visual acuity and TMH using ocular coherence tomography (OCT) 3 times and graded the patients as having mild (>0.7 mm), moderate (0.2 to 0.7 mm) or severe (<0.02 mm) dry eye. Eyes’ TBUT determined normal (>10 s), marginal (5 to 10 s) and low (<5 s) grades of dry eye.

Researchers found that the mean Schirmer’s scores were reduced in smokers’ eyes (22.3±12.61 mm) compared with those of nonsmokers (28.8±0.24mm) (P =.0127). Twenty-four of the 80 eyes of smokers and 10 of the 80 eyes of nonsmokers had Schirmer’s scores <10 mm.

Mean TBUT was less in smokers (9.69±3.96 s) than in nonsmokers (12.8±1.93 s) (P <.0001). Thirty-four of the smokers’ eyes had TBUT <10 seconds while 18 of the nonsmokers’ eyes had TBUT <10 seconds.

Mean TMH was lower among smokers (0.23±0.06 mm) than in nonsmokers (0.36±0.12 mm) (P <.0001). Thirty-eight of the smokers’ eyes (47.5%) had TMH less than 0.2 mm, whereas 12 eyes (15%) of nonsmokers had TMH less than 0.2 mm.

 Mean OSDI was higher in smokers (20.8±15.2) than in nonsmokers (4.03±2.6) (P <.0001). 

Mean central corneal thickness (CCT) was lower among smokers, but the difference was not statistically significant (P =.06).

The researchers said the explanations for their findings may be related to decreased eye nutrition or function of the ocular tissue.

“The toxins associated with smoking induce ischemic changes, including decrease in blood flow or formation of a clot within ocular capillaries,” according to the study. “These ultimately lead to a lack of nutrition essential for eye cell physiology. The lack of antioxidants emerging from peroxidation can lead to a disturbance in the normal functionality of the ocular tissue. Free radicals that are produced because of cigarette smoking cause oxidative stress in proteins, lipids, and cell DNA. Consequently, the cells cannot function normally and ocular diseases develop.”

Limitations of the study included a small sample size, lack of use of tests to assess inflammatory cytokines of the tears and ocular surface, and lack of using lissamine staining.

Reference

Bhutia P, Sen S, Nath T, Shamshad MA. The effect of smoking on ocular surface and tear film based on clinical examination and optical coherence tomography. Indian J Ophthalmol. 2021;69:1693-6. doi:10.4103/ijo.IJO_2840_20