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Reproducibility and repeatability of the OcuSense TearLab™ osmometer.
BACKGROUND:
Some studies report that increased tear osmolarity is a reliable indicator of dry eye syndrome (DES). The OcuSense TearLab™ osmometer requires less than a 100-nl sample of tears and provides an instant quantitative result. Our aim was to clinically evaluate this instrument in terms of its reproducibility and repeatability.
METHODS:
Twenty-nine participants who ranged in age from 19 to 49 years (mean ± SD: 23.3 ± 5.5 years) were recruited. Osmolarity readings were collected by two operators, in two sessions separated by 1 or 2 weeks in order to assess test reproducibility and repeatability.
RESULTS:
The coefficient of reproducibility was 39 mOsms/l; the coefficient of repeatability was 33 mOsms/l.
CONCLUSIONS:
Our mean coefficient of variation over four readings for 29 subjects is 2.9%, which compares well with that reported by the manufacturer. Our results inform practitioners about the level of change over time that can be considered clinically relevant for healthy subjects. This value is 33mOsms/l; any change smaller than this could be attributed to measurement noise.
Some studies report that increased tear osmolarity is a reliable indicator of dry eye syndrome (DES). The OcuSense TearLab™ osmometer requires less than a 100-nl sample of tears and provides an instant quantitative result. Our aim was to clinically evaluate this instrument in terms of its reproducibility and repeatability.
METHODS:
Twenty-nine participants who ranged in age from 19 to 49 years (mean ± SD: 23.3 ± 5.5 years) were recruited. Osmolarity readings were collected by two operators, in two sessions separated by 1 or 2 weeks in order to assess test reproducibility and repeatability.
RESULTS:
The coefficient of reproducibility was 39 mOsms/l; the coefficient of repeatability was 33 mOsms/l.
CONCLUSIONS:
Our mean coefficient of variation over four readings for 29 subjects is 2.9%, which compares well with that reported by the manufacturer. Our results inform practitioners about the level of change over time that can be considered clinically relevant for healthy subjects. This value is 33mOsms/l; any change smaller than this could be attributed to measurement noise.
Eperjesi F, Aujla M, Bartlett H.
Source
Ophthalmic Research Group, School of Life and Health Sciences, Aston University, Birmingham, B4 7ET, UK, f.eperjesi@aston.ac.uk.
A new paper that just published (http://www.ncbi.nlm.nih.gov/pubmed/22475641) shows that tear osmolarity actually has the least variability and highest resolution of all the common dry eye signs over three months, despite it fluctuating faster than the other signs. It's important not to confuse speed of fluctuation with resolution of measurement. Moreover, the new study corroborates historical data, such as Nelson & Farris' study from 1988 that showed how upon *effective* treatment, the variability tear osmolarity is eliminated, and people can return to a homeostatic tear film.
The data also shows that hyperosmolar subjects typically reduce their osmolarity many months before their symptoms improve, up to 3 months beforehand, whereas staining, TBUT, Schirmer's etc., lagged BEHIND symptoms.
So certainly, tear osmolarity is certainly not just a marketing gimmick. It is, however, often difficult to understand statistically, which is why it is important that the doctor take into consideration all data at their disposal. More and more, we're finding that people who thought they had dry eye, but exhibit repeatedly low, stable tear osmolarities don't feel better when they are treated for dry eye because they didn't have dry eye to begin with. Conversely, as the new Cornea paper (http://www.ncbi.nlm.nih.gov/pubmed/22475641) shows, people with "classical" hyperosmolar dry eye can be managed, although perhaps not cured, if they comply with their doctor's instructions.