Bacteriostatic Effect of Multidose Preservative-free Buffered Saline Used in Scleral Lens Wear

Scleral lenses have become an increasingly common treatment for ocular surface disease and irregular corneas. Multidose, preservative-free saline solutions are frequently used off-label to fill scleral lenses. Because the fluid resides over the ocular surface during lens wear, contaminated solutions may increase the risk of infectious complications.

We sought to assess the viability of skin microorganisms and pathogens associated with keratitis once introduced into a multidose preservative-free saline (MDPFS) solution containing the bacteriostatic agent boric acid (PuriLens Plus; The Lifestyle Co., Inc., Freehold, NJ).

Eleven bacterial and one yeast isolate were each inoculated to three lots of MDPFS as well as to sterile normal saline for comparison. Microorganism concentrations were enumerated at baseline and days 1, 3, 7, 14, 21, and 28. Persistence of microorganism viability was compared between MDPFS lots and between MDPFS and normal saline for each organism.

Duration of microorganism viability was ≥24 hours in MDPFS with no significant difference in the distribution of survival duration of microorganisms in MDPFS versus normal saline (P = .15). Candida albicans concentrations declined 14 days earlier in MDPFS, whereas concentrations of viable organisms in MDPFS remained within 1 log of baseline for the longest durations for Pseudomonas aeruginosa (7 days), Escherichia coli (14 days), and Achromobacter xylosoxidans (≥28 days). Gram-positive organism concentrations remained within 1 log of baseline for no more than 3 days. Mild lot-to-lot variation in organism concentrations was noted near the end points of viability. Bacteriostasis was demonstrated in that concentrations of all organisms remained at or below baseline levels throughout the 28-day period.

After microbial contamination, persistence of organism viability was similar in PuriLens and normal saline. Environmental gram-negative organisms, many of which can contribute to infectious keratitis, can persist for weeks once introduced into saline solutions.