Dry Eye Dx and Tx
Smoke Gets in Your Eyes
By William Townsend, OD, FAAO
In 2007, for the first time in decades, less than 20 percent of the population in the United States smoked. The trend continues; in 2010 19.3 percent of adults smoked (U.S. Centers for Disease Control, 2011). Cigarette smoking has long been recognized as deleterious to health; half of all adults who continue to smoke will ultimately die from smoking-related causes.
Smoke and the Ocular Surface
More recently, smoking has been associated with several ocular conditions including lens opacities/cataract, age-related macular degeneration, and thyroid-associated orbitopathy. Lin et al (2010) reported that smokers were more than twice as likely to develop ocular inflammation. Fletcher (2010) suggested that the production of free radials caused by ultraviolet radiation and smoking is a significant risk factor for developing cataracts.
In clinical practice I have anecdotally noted that smokers seem to have a higher incidence of ocular surface disease in general and dry eye specifically. I was interested to see what evidence-based literature has to say about this association. Ward and coworkers (2010) exposed 12 contact lens wearers and 10 non-lens wearers to cigarette smoke for five minutes in a controlled chamber. Prior to exposure, both groups were evaluated for tear evaporation rate, tear breakup time (TBUT), and vital staining. At baseline, the contact lens wearers had significantly poorer scores on all parameters compared to controls. After exposure, TBUTs decreased in both groups, and tear evaporation and vital staining scores increased in controls, but not in the lens wearers. The authors concluded that even brief exposure to cigarette smoke deleteriously affects the ocular surface.
Grus et al (2002) used electrophoresis to evaluate the tear proteins in smokers, severe smokers (more than 20 cigarettes/day), and non-smokers. The subjects were also questioned about subjective symptoms such as burning, itching, foreign body sensation, dryness, and photophobia. Finally, each subject was tested for basal tear secretion. The researchers found that the electrophoresis values for main tear proteins were similar in all groups. In severe smokers, electrophoresis showed additional protein peaks in the range of 20 to 50 KDa not found in smokers and controls. Basal tear secretion was reduced in both smoker groups compared to controls. This study suggests that smokers have additional proteins in their tears not found in non-smokers that may influence the ocular surface. It also reveals that smokers have reduced tear secretion.
Altinors et al (2006) evaluated the influence of smoking on the lipid layer. Sixty smokers and 34 controls took part in the study. They evaluated the ocular surface using corneal and conjunctival sensitivity, fluorescein staining, TBUT, Schirmer 1 test, and conjunctival impression cytology and used tear film interferometry to study the tear film. There was no statistically significant difference in the Schirmer test scores or the TBUT scores, but interferometry of the lipid layer showed marked changes in the tear film not seen in controls. Corneal and conjunctival sensitivity in the controls was statistically significantly higher than in the smokers.
These studies represent only a small segment of research directed toward the impact of smoking on the ocular surface. They give us yet more reasons to encourage smoking cessation, but they also demonstrate that the anecdotal differences we see between smokers and non-smokers have some evidence behind them. Finally, we should recognize that individuals who smoke and want to wear contact lenses may have more problems because of alterations in tear proteins and lipids and advise them appropriately. CLS
To obtain references for this article, please visit http://www.clspectrum.com/references.asp and click on document #191.
Dr. Townsend is in private practice in Canyon, Texas and is an adjunct professor at UHCO. He is president of the Ocular Surface Society of Optometry. He also is an advisor for Alcon, B+L, Vistakon, and CooperVision. You can reach him at email@example.com.