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Abstract. Purpose: To study the effect of environmental toxins on the ocular surface in persons travelling through highly polluted areas of the metropolis of Delhi. Methods: A total of 500 apparently healthy volunteers recruited from the metropolis of Delhi were examined to establish the frequency of ocular surface disorders. All subjects underwent a slit-lamp examination, tear break-up time (BUT) test, Rose Bengal test, Schirmer's test and tear lysozyme level test. Results: Subjects in the study group had significantly higher levels of ophthalmic symptoms compared to the control group. In all, 105 (42%) and 125 (50%) subjects in the study group compared to 50 (20%) and 65 (26%) in the control group complained of redness and irritation (p < 0.05). There was no significant difference in visual acuity (VA) between the two groups, with best corrected VA being 6/9 or better in 92% of the study group and 96% of the control group. The average (± standard deviation) Schirmer's test result was 13.42±6.67 mm in the study group compared to 15.95±6.14 mm in the control group. This difference was statistically significant. The BUT was also significantly lower in the study group (12.97±6.12 seconds) compared to the control group (19.23±5.70 seconds) (p < 0.001). The Rose Bengal test and tear lysozyme activity did not show any significant difference between the two groups. Conclusion: According to our study, environmental conditions appear to have a very significant effect on the ocular surface. There were very high levels of subclinical ocular surface changes among persons travelling in highly polluted areas. [ABSTRACT FROM AUTHOR]