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To the Editor While Bunya et al1 have properly identified variability with the described instrumentation that calls into question its utility as a clinically useful device, these same factors as well as others2 are also valid when using tear film osmolarity for ocular surface research. Their experiences and conclusions are consistent with the work of our laboratory as well as previously published work1-4 all revealing tear volume, evaporation, and blinking effects, which can alter osmolarity. I note that the study was conducted during a period that included spring, summer, fall, and winter climatic conditions where East Coast external environmental exposure may well have affected osmolarity readings.3 The internal environment relating to temperature and humidity was not held constant, nor was there a constant acclimation period for all participants prior to testing. As a person transitions from one environment to another, the time required for the ocular surface and its osmolarity to stabilize may vary from individual to individual and is dependent on the differences from the external to the testing environment, neither of which were standardized. Standardization of testing techniques would remove these variables. Intersession variability was noted, while blink-to-blink intervals,4 incomplete blinking,3,5 and open-eye timing during instrument application were not held constant. Thus, alterations in the tear film dynamics may have varied during the time in which osmolarity measurements were obtained and we cannot assume that the reestablishment of the tear film and its associated osmolarity do not vary with incomplete or erratic blinks. Was there never a time when the probe unintentionally impacted the eyelid margin, conjunctiva, or both, stimulating reflex tears that altered the osmolarity reading obtained? Control of these factors will increase the reliability of subsequent interpretation. The ability of asymptomatic participants to maintain open-eye status without subsequent blinking is grossly different from that of participants diagnosed as having dry eye, and prolonged open-eye intervals may effect tear stability and thus osmolarity in subsequent blinks. Until tear osmolarity readings are shown to be objective, reliable, and repeatedly accurate and are obtained under controlled circumstances, their contributions to our understanding of the physiopathology of dry eye disease remain questionable.
Aquavella JV. Accuracy, Reliability, and Consistency in the Collection of Tear Film Osmolarity Data. JAMA Ophthalmol. 2015;133(12):1482–1483. doi:10.1001/jamaophthalmol.2015.3863
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