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Abstract: Performance of a new small-sample osmometer

Cornea. 2009 May 30. [Epub ahead of print]
Evaluation of a New Tear Osmometer for Repeatability and Accuracy, Using 0.5-muL (500-Nanoliter) Samples.

Yildiz EH, Fan VC, Banday H, Ramanathan LV, Bitra RK, Garry E, Asbell PA.
*Department of Ophthalmology; daggerThe Henry Dazian Department of Chemistry, Mount Sinai School of Medicine, New York, New York; and double daggerAdvanced Instruments, Inc., Norwood, Massachusetts.

PURPOSE:: To evaluate the repeatability and accuracy of a new tear osmometer that measures the osmolality of 0.5-muL (500-nanoliter) samples.

METHODS:: Four standardized solutions were tested with 0.5-muL (500-nanoliter) samples for repeatability of measurements and comparability to standardized technique. Two known standard salt solutions (290 mOsm/kg H2O, 304 mOsm/kg H2O), a normal artificial tear matrix sample (306 mOsm/kg H2O), and an abnormal artificial tear matrix sample (336 mOsm/kg H2O) were repeatedly tested (n = 20 each) for osmolality with use of the Advanced Instruments Model 3100 Tear Osmometer (0.5-muL [500-nanoliter] sample size) and the FDA-approved Advanced Instruments Model 3D2 Clinical Osmometer (250-muL sample size).

RESULTS:: Four standard solutions were used, with osmolality values of 290, 304, 306, and 336 mOsm/kg H2O. The respective precision data, including the mean and standard deviation, were: 291.8 +/- 4.4, 305.6 +/- 2.4, 305.1 +/- 2.3, and 336.4 +/- 2.2 mOsm/kg H2O. The percent recoveries for the 290 mOsm/kg H2O standard solution, the 304 mOsm/kg H2O reference solution, the normal value-assigned 306 mOsm/kg H2O sample, and the abnormal value-assigned 336 mOsm/kg H2O sample were 100.3, 100.2, 99.8, and 100.3 mOsm/kg H2O, respectively.

CONCLUSIONS:: The repeatability data are in accordance with data obtained on clinical osmometers with use of larger sample sizes. All 4 samples tested on the tear osmometer have osmolality values that correlate well to the clinical instrument method. The tear osmometer is a suitable instrument for testing the osmolality of microliter-sized samples, such as tears, and therefore may be useful in diagnosing, monitoring, and classifying tear abnormalities such as the severity of dry eye disease.