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PURPOSE. To establish whether the status of the pre-contact lens tear film as indicated by standard, clinical observational techniques is affected by moderate stimulation of the contralateral eye. METHODS. Four indicators of tear film behavior, lipid layer appearance, amount of debris, inferior meniscus height and non-invasive tear break up time (NIBUT) were monitored in ten subjects before and during 30 minutes of monocular pHEMA contact lens wear. Concurrently, the contralateral eye was either subjected to moderate irritation by means of a silicone elastomer contact lens, or remained unstimulated. Data were compared, between the stimulated and unstimulated states to identify evidence of contralateral treatment effects. RESULTS. After 30 minutes, maximum contralateral differences between the unstimulated and stimulated conditions were 1 grade for both lipid layer appearance and debris, 0.1 mm for meniscus height and 4 secs for NIBUT. CONCLUSIONS. The magnitudes of contralateral effects induced by moderate, monocular irritation were comparable with the within-subject variabilities associated with these indicators of tear film behavior. [ABSTRACT FROM AUTHOR]