These preservatives degrade in the tear film, which theoretically minimises ocular toxicity. However, as with detergent preservatives, patients with DED may not have sufficient tear volume to complete the degradation and may experience irritation. (3)
Having discussed the importance of keeping the drops free from contamination yet trying to avoid, as much as possible, the negative effects of preservatives, one approach would be to physically keep the product free from contamination. Unit/single dose or single day vials can be preservative free as they are designed to (and must) be discarded immediately after use or on the day of use.
More drop bottles are now being designed with specially engineered valves and/or micro-filters that allow the drop fluid out, but don’t allow micro-organisms in. The design of the drop container should be thought through; it is important for patients, many of whom are older with restricted finger pressure and dexterity to be able to express a drop. Most manufacturers will be acutely aware of this and design containers with it in mind. Some patients prefer a spray alternative.
Generally, these are preservative free, although they don’t necessarily offer all the optional ingredients discussed earlier.