Purpose: Preservatives are essential for preventing contact lens (CL)-related microbial keratitis (MK). The purpose of this review is to summarize the current knowledge related to the use of common ophthalmic preservatives in CL care products with respect to both safety and efficacy. Methods: Manuscripts written in English were obtained by searching PubMed.gov with the term contact lens plus antimicrobial, benzalkonium chloride, biguanide, Aldox, polyquaternium, preservative, thimerosal, EDTA (ethylenediaminetetraacetic acid), chlorhexidine, or blister pack. Results: This review found that first-generation preservatives are no longer used in CL multipurpose solutions (MPS) due to their high levels of ocular toxicity. Modern, highmolecular-weight preservatives, including polyquaternium-1 (PQ-1) and biguanides (PHMB), are generally effective against bacteria, minimally effective against fungi, and not effective against Acanthamoeba. PQ-1 and PHMB are likely safe when used with CLs, but they may cause ocular adverse events, with roughly equal risk between the two preservatives. Some CL MPS contain both PQ-1 and PHMB, but no increased risk of adverse events has been reported when combining the two. Hydrogen-peroxide (H 2 O 2 ) solutions are effective against all common ocular microbes, including Acanthamoeba, and they have been proven safe with proper compliance. Povidone-iodine (P-I) solutions are not currently commercially available in North America, but they have been shown in other countries to be safe and effective. Conclusion:Patients should be monitored when using PQ-1 or PHMB-containing solutions since they have been associated with ocular adverse events. If events are detected, patients should be switched to an alternative solution. H 2 O 2 or P-I solutions are preferred for any patient who may expose their CLs to water because they are the only solution categories effective against Acanthamoeba.

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