The Dry Eye Zone

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Abstract: Retention time of drops in the eyes

Much as I suspected: artificial tears, even thick ones, ain't all that much better than saline :) Yes, I know that that wasn't the point of the study.

Retention and retention of effect of topical formulations in dry eye subjects.
Optom Vis Sci. 2008 Sep;85(9):873-9. Links
Paugh JR, Nguyen AL, Huang P, Hwang JS.

PURPOSE: It was the purpose of this investigation to examine both retention time (RT) and retention of effect of two ophthalmic formulations in the same dry eye subjects.

METHODS: This was a randomized, subject-masked cross-over study. Dry eye subjects, characterized by sub-type, were recruited. For direct RT measurement, fluorescein isothiocyanate (FITC)-dextran, 70 kDa molecular weight, was admixed at 0.1% wt/vol concentration into buffered saline (active control) and a viscous marketed artificial tear formulations (test formulation). RT in minutes was estimated directly as the return to baseline intrinsic fluorescence with an objective scanning fluorometer. Retention of effect was measured with a xeroscope as non-invasive breakup time (NIBUT) and by use of a numerical rating scale for comfort.

RESULTS: Eleven subjects, with most being classified as having non-inflammatory meibomian gland dysfunction, completed the study. The RTs averaged 17.7 (+/-10.0) and 26.8 (+/-16.5) minutes for the saline and test formulations, respectively. The averages for NIBUT were 8.73 (+/-6.1) and 19.5 (+/-4.9) minutes, for saline and the test formulations, respectively. Return to baseline for the numerical rating scale comfort averages were 9.91 (+/-4.1) and 20.21 (+/-6.4) minutes for the saline and test formulations, respectively. When residence time was subtracted from the retention of effect measures, no statistical significance was found for the polymeric solution (vs. comfort, p = 0.153; vs. NIBUT, p = 0.109). However, statistical differences were found for direct retention compared against comfort (p = 0.01) and NIBUT (p = 0.004) for buffered saline.

CONCLUSIONS: It seems that these two retention of effect measures are much shorter than RT measured directly. Future work should aim to confirm these findings in additional dry eye sub-types and in those with more severe disease manifestations.