Mr. editor

This letter concerns the article titled “Ophthalmic Preservatives Common in Soft Contact Lens Care Products: Benefits, Complications, and Comparison to Preservative-Free Solutions”.¹

We read this article with great interest and thank the authors for providing an excellent review on current preservatives in multipurpose solution (MPS) products for soft contact lenses. For the sake of rigor, we would like to add some elements not mentioned in the article which support the conclusions of the authors advocating the use of solutions without preservative.

Several in vitro and in vivo studies have demonstrated that polyvalent solutions (MPS) containing polyquaternium-1 are inflammatory and induce oxidative stress to ocular surface cells to varying degrees.² In addition, polyquaternium-1 damages the barrier function of corneal epithelial cells by affecting the localization of ZO-1 at tight junctions in response to the secretion of Tumor Necrosis Factor Alpha (TNF-α).² Additional research has shown that some MPSs containing PHMB and borate exhibit amplified corneal staining and are detrimental to the comfortable wearing of soft contact lenses, especially in specific combinations of lenses and solutions.²

The authors highlight the complexity of the effect of preservatives in vivo, which can be influenced by the type of lens. As scleral lens wear has grown worldwide, we would like to draw attention to the possible influence of these preservatives in this environment. While the preferred accepted recommendation is to fill the lens with a preservative-free saline solution and disinfect it with peroxide (H2O2) products,³ many clinicians and patients have switched from this formula to disinfecting with alternatives or using a more viscous fluid for lens filling.⁴ This modification is preferably also preservative-free, but sometimes includes MPS formulas initially intended for the use of soft lenses, in 3 to 7% of the wearers in a study.⁴ The reasons for this are wettability issues, or an attempt to resolve the “midday fog”, caused by many possible etiologies.^3.4 This can potentially cause a corneal response.³ As mentioned in the article, the combination of ingredients in a solution and the combination of a solution with a particular lens material may be relevant for the development of corneal staining, or, as discussed in Alves et al,⁵ affect the optical properties of the lens. While this may not directly be the exclusive result of the preservative in MPS and also associated with biochemical and biophysical interactions, the H2O2 product was more resistant to change when combined with a variety of materials.⁵ While these influences have not yet been examined in the scleral lens environment, they may or may not be of clinical importance there as well. These considerations should evoke careful deliberation, carefully weighing the pros and cons while awaiting a recommendation to use an MPS with scleral lenses.