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B. Martin-Martin, F. Blazquez, A. Mayo, N. Laguna, A. Anton; Volume and Variability of Hypotensive Eyedrops . Invest. Ophthalmol. Vis. Sci. 2003;44(13):2190.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: The approximate capacity of the lower conjunctival sac is 30 µl. The aim of this study is to assess the drop volume of the different commercial antiglaucoma medications eyedrops available in Spain. Methods: A hundred and fifty bottles, ten of each of commercial hypotensive eyedrops available in Spain were examined. Samples from two different shipments from each medication were used when available, so that variability between shipments of the same drug could also be assessed. In order to evaluate the possible variability of the drop volume as the bottle is being emptied in a normal usage, drop samples were taken at different usage moments: out of the box, half empty and almost empty. The mass of five drops from each usage moment of the bottle was measured. Their volume was then calculated using an average density provided by the evaluation of the first two bottles of each medication. Every evaluated drop was expelled in the same conditions: room temperature, handling angle (90° from the horizontal), and expelling technique. All the evaluation wsa performed by the same investigator (B.M.). The variability of the drop volume from each bottle was evaluated with variance and variation coefficient. Comparison of variance between bottles of the same drug, and between different medications was performed. Results: Drop volume varied significantly between drug manufacturers, ranging from 22.26 µl to 38.02 µl. Variability attributable to different shipments of the same drug was not found. The drops from the beginning, the middle and the end of the bottle within the same bottle didn't offer significant differences. The variability attributable to differences between manufacturers was approximately 15 times greater than the one attributable to differences within the same brand. Conclusions: The 86.7% of the commercial hypotensive eyedrops included in this study had a mean volume under 30µl. Differences up to 100% between mean drop volumes associated to drug type were found.
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