It is well understood that using inappropriate saline solutions to fill scleral lenses can result in corneal insult (Figure 1). Studies have indicated that tear exchange under sclerals is present but relatively slow (Tan et al, 2018; Tse et al, 2019). Thus, it is critical that the fluid reservoir is free of potential irritants to the ocular surface.

The Scleral Lenses in Current Ophthalmic Practice: an Evaluation (SCOPE) Study surveyed scleral practitioners and reported that the majority of respondents recommended preservative-free saline for application, including both single-use vials or bottled products (Harthan et al, 2018). When contemporary sclerals first began to gain popularity, the available filling solutions were limited to off-label products not specifically intended for scleral use. Some of the earliest solutions utilized were preservative-free sodium chloride 0.9% inhalation solution vials and multidose saline bottles. While there were no widespread reports of clinically significant issues with these off-label products, the industry recognized the need for development of solutions explicitly for use with scleral lenses. There are now several commercially available preservative-free saline solutions that have been approved for scleral lens use by the U.S. Food and Drug Administration.

Considerations

1) Single-Use Vial versus Multidose Bottles Single-use vials are popular for scleral lenses due to their portability and reduced risk of contamination. However, some patients may prefer multidose bottles that are recommended to be discarded within 15 days after opening. When considering the safety of multidose bottle use, Chiu (2020) reported that the majority of patients demonstrated some type of risky behavior that could increase bottle contamination. The overall rate of contamination was 62.9%, with 21 distinct pathogens identified; but this contamination did not correlate with greater incidence of microbial infections (Chiu, 2020). Patients who may need a greater volume of saline for rinsing and filling may prefer the multidose bottle.

2) Buffers Borate and phosphate buffers are often included in ophthalmic solutions to balance pH; one proposed benefit is that the pH is closer to that of natural tears. Commercially available pH values of scleral salines range from ~5.3 to 7.4. A small case series of five dry eye scleral wearers showed that 80% preferred buffered over non-buffered saline, possibly due to pH differences (Caroline and André, 2019).

In a study by Houlsby et al (1986), borate-buffered agents had an antimicrobial effect, suggesting another potential benefit. However, the kill rate of the buffer alone was slow and did not meet the U.S. Pharmacopeia preservative effectiveness test.

There have also been arguments made that buffers themselves can be irritating to a patient. Schuerer et al (2017) demonstrated cytotoxicity of various buffers to the human corneal-limbal and conjunctival cells that increased with higher concentration and longer contact time, but this histological analysis did not take into consideration blinking and tear dynamics that would be translatable to a clinical setting. Looking at scleral lens wear specifically, a study from Tse et al (2020) showed no significant difference in corneal health impact when comparing buffered versus non-buffered solutions. It appears that either solution type can be used successfully by many patients. When troubleshooting a comfort issue, consider switching saline.

3) Unique Formulations One of the most recently developed products sets itself apart as the only saline containing electrolytes that mimic the components of natural tears. It has been suggested that this can improve symptoms of dryness and blurry or fluctuating vision. As scleral prescribing continues to grow, it is conceivable that more solution innovations will arise to better serve this specialty lens population. CLS

For references, please visit www.clspectrum.com/references and click on document #304.