Purchase this article with an account.
G. H. Bennett, P. W. Kramer, T. Cappo; A New Method to Measure Tear Osmolarity in Diagnosing Dry Eye Disease- Surface Plasmon Resonance Nanoliter Tear Osmometer. Invest. Ophthalmol. Vis. Sci. 2007;48(13):429.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
A new user-friendly technique for measuring tear film osmolarity to aid in diagnosing dry eye syndrome (DES).Tear osmolarity due to its sensitivity and specificity as a single test modality may be a possible gold standard to determine DES.
A prototype nanoliter tear osmometer was developed using chemical sensor technology, Surface Plasmon Resonance (SPR). The device uses light from a laser diode that interacts with a metal sensing surface and tear film to determine fractional changes in tear osmolarity. The laser light is incident on a metal dielectric interface at a particular angle, and the reflected light is extinguished. The light not reflected is absorbed by the sensing surface creating a resonance effect of electrons in the metal surface. A photodetector senses image changes when solutions of different osmolarity are applied to the sensing surface. Known salt solutions with osmolarities within physiological range and human tears were tested. Tear samples (100-400 nanoliters) were extracted using a capillary micropipette. Two solutions of known osmolarity were placed on the sensing surface for calibration, and human tear sample was placed in between the two known samples.
Instantaneous changes in image characteristics were detected upon contact of test solutions on sensing surface and images were analyzed by software and displayed as a characteristic curve.Solutions of different osmolarities show each measurement as a curve along the x-axis. The shift in the curve was linearly proportional to changes or differences in osmolarity.Examples:Known salt solutions with osmolarities of 300, 315 and 330mOsm/L compared to water (0) mOsm/L demonstrate shift along x-axis. Human tear sample = 315.1 mOsm/L (left eye) and 324 mOsm/L (right eye)using known salt solutions of 315mOsm/L and 330 mOsm/L for calibration. Suggestive evidence of repeatability and sensitivity demonstrated by testing multiple known salt solutions of 330 mOsm/L and 315 mOsm/L on sensing surface.Measurements = 329.7, 329.9 and 330 mOsm/L and 313.4, 314.3 and 315 mOsm/L.
The increased prevalence of DES is driving the need for a single gold standard test to aid in diagnosing DES and following new drug treatments introduced to treat DES.Freezing point methods have been unsuitable for clinical use.The technique of determining tear osmolarity with SPR, may provide a method that is user-friendly with instantaneous sensitive measurements. Future controlled studies comparing SPR and freezing point depression techniques are needed to evaluate this new method of determining tear film osmolarity.
This PDF is available to Subscribers Only