Preserved artificial tears are the kind you buy in a bottle. Unpreserved artificial tears are the kind you buy in sets of tiny little single-use vials.

Generally speaking, you will be told (or if you’re not, you should be) that for constant use you should use unpreserved artificial tears. This is because most artificial tears in a bottle are preserved with benzalkonium chloride, which can build up in your eyes and cause irritation or allergic reactions.

This does not mean that everything in a bottle is off limits. Exceptions include Systane, which uses a preservative that dissipates when the drops are applied, and the Aqueous Pharma product line (Dwelle, Dakrina, Nutratear/Redkote, Freshkote) which contain a patented preservative (Busan 1507) that does not irritate the eyes.