Abstract
Purpose: :
To evaluate the effect of environmental air pollution levels on tear film osmolarity and to investigate the correlation between lacrimal osmolarity and clinical signs and symptoms related to the ocular surface.
Methods: :
Twenty-four healthy male volunteers who work either as taxi drivers or as traffic controllers in São Paulo, a city with high levels of air pollution, were prospectively studied. Subjects carried passive sampler equipments to register nitrogen dioxide (NO2) and particulate matter (PM2,5) levels in order to use as indicators of their exposure to air pollution. The subjects were instructed to keep the passive samplers during 24 hours/day starting at 8 o’clock a.m.. The following day, subjects were submitted to: ocular surface disease index (OSDI) questionnaire, Schirmer test, tear film break up time (TFBT), corneal and conjunctival vital staining with fluorescein and lissamine green and osmolarity essays. The same procedures were repeated after 2 weeks in order to evaluate possible variations in air pollution exposure.
Results: :
Subject’s age ranged between 31 and 65 years old (46.79 ± 9.7 years), the ambient temperature between 17,4 and 22,4ºC and humidity between 52 and 76%. Mean values of NO2 and PM2,5 levels were 179.74 and 40.49 µg/m3, respectively, at the first exanimation and 216.86 and 33.81 µg/m3, respectively, at the second examination. Tear film osmolarity levels (mean ± standard deviation, mOsmol/kg) were 298.56 ± 23.19 and 303.72 ± 23.52 at the first and second evaluation respectively. There was no significant correlation between the OSDI score, findings on the Schirmer test or corneal and conjunctival vital staining and NO2 and PM2,5 levels. However, a significant and negative correlation between TFBT and air pollution levels (p<0,05) was observed. Moreover, there was a significant and negative correlation between PM2,5 levels and tear film osmolarity levels. Each increase of 5,5 µg/m3 in PM2,5 was associated with a decrease in 10 mOsmol/kg in tear osmolarity (p<0,05). There was a negative, but not significant (p>0.05) correlation between NO2 and tear osmolarity.
Conclusions: :
Although there is frequently a lack of correlation between reported symptoms and finding on ophthalmic examination, our study indicates that an increase in air pollution levels can be associated with an increase the tear film instability. An increase in exposure to PM2,5 levels is associated with a decrease in tear film osmolarity. Tear osmolarity seems to be an useful laboratory parameter to investigate ocular surface adverse effects associated with high levels of exposure to ambient air pollution.
Keywords: ocular irritants • ocular irritancy/toxicity testing