I have a strong love-hate relationship with lens solutions. Even the seemingly straightforward scleral lens (SL) filling solutions can become an area of concern. I have encountered patients who fill their SLs with multipurpose solution, tap water, or even GP conditioner before applying them. Is a stern reminder to avoid preservatives enough to prevent complications?
Preservative-Free Does Not Mean Problem-Free
Preservative-free SL filling solution has literally been keeping me up at night; we recently published a study detailing microbiological findings in 4oz saline bottles used for SL wear (Chiu et al, 2020), and our results were far from sterile (Table 1). How commonly do patients use multidose preservative-free saline (MDPFS) to fill their SLs?
|GRAM-POSITIVE (7) (N = 26)|
|Diphtheroid, NOS (1)|
|Kocuria kristinae (1)|
|Micrococcus luteus (1)|
|Staphylococcus epidermidis (9)|
|Staphylococcus haemolyticus (2)|
|Staphylococcus pasteuri (4)|
|Staphylococcus warneri (8)|
|GRAM-NEGATIVE (14) (N = 20)|
|Acinetobacter ursingii (2)|
|Citrobacter freundii (1)|
|Delftia acidovorans (1)|
|Enterobacter cloacae complex (1)|
|Escherichia coli (1)|
|Klebsiella (Enterobacter) aerogenes (1)|
|Klebsiella oxytoca (2)|
|Klebsiella pneumoniae (2)|
|Ochrobactrum anthropi (1)|
|Pluralibacter gergoviae (1)|
|Pseudomonas aeruginosa (1)|
|Pseudomonas fluorescens (2)|
|Serratia marcescens (3)|
|Stenotrophomonas maltophilia (1)|
|Abbreviations: NOS = Not otherwise specified (no identification by MALDI-TOF)|
The Dry Eye Foundation conducted a survey in 2018 in which SL-wearing patients were asked “Which saline do you use most frequently to fill your lenses?” Of the 219 answers received, one brand of MDPFS was by far the most common response (105 respondents, 49%).
MDPFS is often used off-label to rinse and fill SLs prior to lens application. The manufacturer of the one in the survey recommends discarding the bottle and contents 15 days after opening. This was not designed with SL wear in mind, and due to the non-bactericidal nature of this saline, microorganisms may persist for days or weeks once introduced.
How easy is microorganism introduction? These bottles are designed with a raised neck and nozzle and are sealed until punctured. Sweeney et al (1992) found that saline bottles of this design showed no microorganism growth even when left open near a toilet for an hour every day over a four-week period. Therefore, microorganism introduction must somehow be related to patient handling and use of these bottles. Prior saline studies also report that bottle contamination may arise with normal use (Sweeney et al, 1992) or with poor management of lens care (Willcox and Holden, 2001; Szczotka-Flynn et al, 2010; Arshad et al, 2019; and others; full list available at www.clspectrum.com/references ).
The good news is that MK is a rare complication among SL wearers (Schornack, 2015; Fadel and Toabe, 2018a and 2018b), and the causative factor in some reported cases appears to be overnight storage of SLs in saline (Fadel and Toabe, 2018b). But, the disease process is incredibly multifactorial, and pinpointing the exact source of infection is a daunting task.
Steps to Prevent Infection
What is clear, however, is that patient education on proper MDPFS bottle handling as well as SL storage and hygiene to decrease contamination must be emphasized. For patients who have a history of MK or severely compromised corneas, consider a unit-dose preservative-free saline solution or even a nutrient-rich filling solution designed specifically for specialty lens wearers. CLS
For references, please visit www.clspectrum.com/references and click on document #297.