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Constanca Coelho, Fernanda Azancoth; In vitro evaporation rate and stability of four marketed artificial tears. Invest. Ophthalmol. Vis. Sci. 2013;54(15):6026. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
To assess the in vitro evaporation rate and precipitation of four marketed artificial tears: Purite® 0.1mg preserved sodium carboxymethylcellulose (Na-CMC) 0.5%+glycerin 0.9% (Optive®), Polyquad 0.001% preserved polyethylene glycol (PEG) 400 4mg+propylene glycol (PG) 3mg (Systane Ultra®), ethylenediamine tetraacetic acid (EDTA) 0.1% preserved sodium (Na) hyaluronate 0.15% (Opticol®), preservative-free trehalose 3% (Thealoz®).
1 ul of each artificial tear was placed on a hemacytometer and allowed to stand, at normal room pressure, temperature and humidity, up to 48h. Drops were inspected under a reverse phase microscope at regular intervals, and photographs were taken at 0h, 5 min, 4h, 6h, 8h, 24h and 48h. All drops were analyzed simultaneously. Evaporation and precipitation percentages were calculated based on the hemacytometer scale.
EDTA 0.1% preserved Na-hyaluronate 0.15% completely evaporated and precipitated after 5 minutes, generating a disorganized lattice of crystals. All other drops showed an initial evaporation at 4h varying between 45.6% and 70.5% (preservative-free trehalose 3% < Purite® 0.1mg preserved Na-CMC 0.5%+glycerin 0.9% < Polyquad 0.001% preserved PEG 400 4mg+PG 3mg), which did not change up to 24h. From 24h to 48h the evaporation percentages increased between 2.1% and 4.5%. The two formulations with preservatives started to precipitate after 4h, reaching between 15.7% and 15.8% precipitation after 48h. The Purite® 0.1mg preserved Na-CMC 0.5%+glycerin 0.9% generated a lattice of crystals with some degree of organization, whilst the Polyquad 0.001% preserved PEG 400 4mg+PG 3mg showed a concentric precipitate with an apparently organized crystallized border. The preservative-free trehalose 3% formulation did not precipitate or crystallize up to 48h.
Given the purpose of any artificial tear is to stabilize the tear film and protect the corneal surface, they should be stable solutions, with a low vapor pressure. Based on the evaporation rates, results suggest that the analyzed artificial tears will remain in contact with the eye surface during a period of time that will follow the order Thealoz® > Optive® > Systane Ultra®, with Opticol® evaporating almost instantly. Thealoz® was the only drop that did not precipitate or crystallize up to 48h, suggesting it is more stable than the other tested drops.
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