Multi-use eye drop products contain preservatives to prevent microbial growth. The most common agent used in manufacturing is benzalkonium chloride (BAK). But this substance raises health issues, especially in cases of dry eye disease.

A special polymer named PQ-1 (Polyquaternium-1) is used as an alternative preservative for both dry eye preparations and glaucoma medications. An anti-bacterial, PQ-1 keeps the product free from pathogens. But because of its larger molecular size, it does not penetrate human cells and drastically lowers the toxic risks compared to BAK.