BAK preservatives are very effective against pathogens, however they were not specifically designed to be friendly to the eye. They can consist of harsh chemicals that stop bacterial growth but also harm corneal and conjunctival epithelial cells.
After chronic use of medications containing these preservatives for conditions such as glaucoma, the deleterious effect on anterior segment epithelial cells leads to poor production and maintenance of the tear film, resulting in problems such as dry-eye syndrome. Long-term use can also roughen the surface of the cornea and conjunctiva because of loss of epithelium and inflammation
These preservatives do a good job of protecting the multidose bottle of medication, but they have the potential for long-term deleterious effects on the eye.
Elara explains using 3d Animation and voiceovers.