In the past decade many bacteriological studies have been pursued on an in vitro scale in an attempt to evaluate activity of proposed ophthalmic preservatives. These included the work of McPherson and Wood1; Skolaut2; Scigliano and Skolaut3; Krause, Dauer, and Guth4; Heller and associates,5 and Murphy, Allen, and Mangiarcine.6 It is apparent from these studies that many of the authors consider bacteriostatic concentrations to be a safe level of preservation for these solutions. Murphy, Allen, and Mangiarcine directly stated that bacteriostatic and fungistatic powers were among the properties to be possessed by an ideal ophthalmic preservative. More recently, Lawrence7 has published a general review of chemical preservatives for ophthalmic solutions. He concludes:
A careful review of the literature reveals that in preparing and dispensing ophthalmic drugs, chlorobutanol, phenylmercuric nitrate, and benzalkonium chloride are considered the bacteriostatic agents most suitable for providing "self-sterilizing" solutions.
RIEGELMAN S, VAUGHAN DG, OKUMOTO M. Rate of Sterilization as a Factor in the Selection of Ophthalmic SolutionsExperimental Studies with a Proposed Method of Preparing Sterile Solutions. AMA Arch Ophthalmol. 1955;54(5):725-732. doi:10.1001/archopht.1955.00930020731016