By Martin Conway
Current scleral lenses are made from the same group of materials that have been used for the manufacture of corneal lenses for years. The cleaning and disinfection solutions used to care for these lenses should therefore, in theory, be suitable for the new wave of scleral designs.
Unfortunately that is not the case, scleral lenses work differently. They form a sealed enclosure behind the lens which means that any solution in the bowl of the lens is retained behind the lens for the duration of the wearing time. Practitioners are aware of this and will advise their patients to rinse any cleaning or disinfecting solution off of the lens with non-preserved saline prior to filling the bowl with fresh saline or one of the new solutions designed for scleral filling. Additional lubricant may be added, again from a non-preserved formulation. This removes the possibility of any epithelial reaction to preservative or irritants within the bowl which, may be innocuous in short-term exposure when used in a corneal lens but, may manifest itself in the longer exposure experienced under a scleral lens.
The confusion practitioners have is with the term “non-preserved”. There are “non-preserved” saline systems on the market that are available in 250 ml containers. This means that as the solution is used, air is drawn back into the bottle. This may contain organisms that could proliferate in the solution over the course of its use and possibly cause an infection if introduced into the eye at a later date. This means that there must be something acting within the formulation of that solution to kill any organism introduced. This was the traditional role of a preservative such as chlorhexidine or thiomersol in the past. So how come the manufacturers are allowed to market these products as “non-preserved”? Well, if another active ingredient in the formulation has the ability to kill these opportunist organisms, then maybe they can claim that the solution does not contain specific preservatives, even though it may contain an aggressive component such as hydrogen peroxide or sodium hyperchlorite, albeit in very low concentrations. In the normal course of use, these formulations are safe if used in accordance with the manufacturer’s instructions. If they are used to fill the bowl of a scleral lens and kept in contact with the corneal epithelium for 12 -16 hours however, then this may not be the use that the original formulation was designed for, and therefore some reaction to the chemicals may be expected.
Another concern that I have is the use of a non-preserved saline in a disinfection unit. These units use UV light to disinfect the lens and sub-sonic agitation to clean the lens. This is fine and appears to be effective. The opened bottle is kept for 15 days (if the patient is compliant). Any contamination of the opened bottle will be dealt with by the subsequent UV exposure, we must presume. In the case of a scleral lens, how tempting will it be for the patient to fill the newly disinfected bowl with solution from their non-preserved solution bottle. At the end of 15 days in a warm environment, quite a bacterial soup could be brewing!
Along similar lines, unit-dose saline can be abused by the patient if the saline is available in larger volumes than necessary for a single use. When training a patient in the application of their scleral lens, the practitioner must inform them of this issue. To avoid unnecessary and risky re-usage of saline. You can get a 30 ml unit dose on the market which I believe is a problem waiting to happen.
In conclusion, practitioners should be wary of any solutions used to fill the bowl of a scleral lens prior to insertion if it is packaged in a reusable bottle, even if the term non-preserved appears on the label. Unit doses are safer, but may pose a risk of non-compliance and subsequent infection if available in larger volumes than absolutely necessary.