Artificial tears are traditionally used to relieve dry eye, from the slightest dryness to the most severe. The chemical composition, in very simple terms, is that of a physiological solution with humectant agents to restore balance to the tear.
The humectant agent that affords the most advantages is undoubtedly hyaluronic acid because of its viscoelastic properties, its water-retaining capacity, its excellent tolerance and because it regenerates the ocular surface.
This might initially seem to be the case. It is true that in an experimental study carried out on mice which compared the efficiency of different humectant drops with concentrations of 0.10%, 0.18% and 0.30%, the conclusion was clear: in all three cases, the signs evaluated improved in comparison with the untreated group and the higher the concentration, the better the results in tear breakup time (TBUT), corneal staining and goblet cell density, amongst others.
But the authors of the study acknowledged that it had limitations in that there is a variable that was not taken into account – comfort, that is, the subjective sensation felt by the contact lens user.
The fact is that the higher the concentration of hyaluronic acid, the greater the possibility that there will be blurred vision and that lubrication will be affected, which may lead to friction with the eyelid and discomfort.
The molecular weight of the hyaluronic acid is also important.
Because the greater the molecular weight of the hyaluronic acid, they greater its viscosity at rest. Hyaluronic acid belongs to the group of fluids called ‘non-Newtonian’, in which viscosity depends on movement. They remain viscous when at rest but are fluid when there is movement. This characteristic is called viscoelasticity and increases with higher molecular weight of the hyaluronic acid.
Viscoelasticity is an ideal property for humectant drops because it allows for formulations that are viscous at rest (when the eye is open) to become fluid when there is movement (blinking).
In fact, the same viscosity can be obtained from a solution of very high molecular weight hyaluronic acid (with half the quantity) as with a solution of low molecular weight hyaluronic acid. So, if the hyaluronic acid has a very high molecular weight, the concentration can be reduced and the same results achieved as with a higher concentration
And why would it be good to reduce the amount of hyaluronic acid?
Because hyaluronic acid at very high concentrations may cause blurred vision and discomfort for the user.
In the Acuaiss family there are drops with different concentrations of hyaluronic acid and in different formats to relieve all cases of dry eye.
Acuaiss Dual Gotas contains 0.13% hyaluronic acid + 0.10% of hydroxyethylcellulose. It is indicated for relieving mild dry eye.
Acuaiss Ultra Gotas contains 0.15% hyaluronic acid and is indicated for chronic, moderate dry eye, especially for contact lens users.
Acuaiss Dual Gel contains 0.30% hyaluronic acid + 0.10% hydroxyethylcellulose and is indicated for relieving moderate dry eye.
All the Acuaiss drops contain high molecular weight hyaluronic acid and bring relief to the symptoms of dry eye without causing blurred vision.
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● Bothner H, Wik O. Rheology of hyaluronate. Acta Otolaryngol Suppl. 1987;442:25-30. doi: 10.3109/00016488709102834. PMID: 3481162.
● Falcone SJ, Palmeri DM, Berg RA. Rheological and cohesive properties of hyaluronic acid. J Biomed Mater Res A. 2006 Mar 15;76(4):721-8. doi: 10.1002/jbm.a.30623. PMID: 16315193.
● You IC, Li Y, Jin R, Ahn M, Choi W, Yoon KC. Comparison of 0.1%, 0.18%, and 0.3% Hyaluronic Acid Eye Drops in the Treatment of Experimental Dry Eye. J Ocul Pharmacol Ther. 2018 Oct;34(8):557-564. doi: 10.1089/jop.2018.0032. Epub 2018 Jul 23. PMID: 30036099; PMCID: PMC6206550.