Abstract
Purpose:
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®).
Methods:
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.
Results:
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.
Conclusions:
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.
Keywords: 486 cornea: tears/tear film/dry eye •
599 microscopy: light/fluorescence/immunohistochemistry •
503 drug toxicity/drug effects