A recent study analyzed the composition of different formulations of atropine, as preservatives such as benzalkonium chloride and the atropine concentration itself may affect the degree of corneal penetration, which is important to consider in myopia treatment.

“Since there’s a trade-off between side effects, stability and optimal effects of atropine on myopia, it’s important to gain better knowledge about intraocular atropine concentrations,” the researchers wrote in their paper. They performed ex vivo studies on freshly enucleated pig eyes to assess corneal penetration of different atropine 0.01% formulas.

From the extracted aqueous humor samples, the researchers determined that the variability in applied drop size exceeded the differences between preserved and preservative-free formulations. “The atropine concentration in the anterior chamber measured after 10 minutes was only 3.8x10-8 of its concentration in the applied eye drops, corresponding to 502.4 pM,” they noted. “Obviously, the preservative didn’t facilitate corneal penetration, at least ex vivo.” They didn’t measure the drop size of the dispensers, however, because “increasing drop size doesn’t result in the penetration of more medication into the cornea.”

Limitations of the ex vivo study included lack of tear flow and tear film turnover. “Our measurements don’t allow any direct conclusions to be drawn about efficacy, nor therefore about the relevant minimum concentration that would be sensible to use, but it can be stated that the presence of the preservative had only a negligible effect on the penetration of a single drop,” the researchers wrote.

They concluded that atropine 0.01% demonstrated good dose-dependent penetration into the cornea and anterior chamber. “It wasn’t significantly affected by additives and preservatives,” they concluded. “Therefore, as long as long-term stability and microbiological safety are considered, appropriately unpreserved ophtioles and vials can be used.”