While most glaucoma patients take at least one eye drop to control eye pressure, as many as 40% of patients need more than one medication.
Ocular surface disease, OSD, (which includes dry eye syndrome) can cause redness, tearing, irritation, burning, foreign body sensation, light sensitivity and intermittent blurred vision. Although 15% of elderly patients describe some degree of OSD, up to 60% of patients with glaucoma suffer from it.
The symptoms mentioned above affect the quality of life and even the adherence to the prescribed medications to help preserve existing vision. The active ingredient of a medication, the component that is used to lower the eye pressure, can cause OSD. It is also known that inactive ingredients, such as preservatives, can contribute to OSD.
Furthermore, the negative effects of preservatives seem to be additive. The more medications a patient takes the more likely he/she is to have symptoms. Preservatives were initially used to kill bacteria in the bottle and it was thought they helped the active ingredient have its desired effect. Since the active ingredient is the component of the medication that lowers the eye pressure, any negative effect it may have is thought to be a necessary evil. For patients with OSD, difficulties tolerating eye medications can possibly be improved by minimizing the effect of preservatives on the ocular surface.
Types of Preservatives
The most common preservative used in eye drops is Benzalkonium chloride (BAK). The effects of BAK have been well studied and it is known to cause inflammation and cell damage. More recently other preservatives including stabilized oxychloro complex (Purite®) found in Alphagan-P (Allergan) and ionic-buffered preservatives (sofZia®) found in Travatan Z (Alcon) have been used. Clinical studies demonstrate improved patient comfort when using the same active ingredient but switching from BAK to Purite® as the preservative. While significantly less toxic than BAK, sofZia® still causes some negative effects and, interestingly, clinical trials have not demonstrated much difference in patient comfort when compared to BAK.
Three medications, timolol, a dorzolamide/timolol fixed combination, and a prostaglandin analog, tafluprost, can be obtained in preservative-free forms. Large clinical studies comparing preservative to preservative-free medications have found that patients experience less irritation and discomfort with these medications. Eyes treated with preservative free medications also appear to have healthier ocular surfaces as determined by their doctors.
I typically find that most patients do fine with one, and often, two medications regardless of whether or not they contain preservatives. However, patients taking three or more medications often experience symptoms of OSD. If I cannot attribute a patient’s adverse symptoms to an allergy I will consider switching to a preservative-free alternative when possible. Unfortunately, the added costs of these medications are often a consideration.
Article by Michael R. Banitt, MD, MHA.
First posted May 14, 2014; Last reviewed on April 19, 2022.
Michael R. Banitt, MD, MHA
Dr. Banitt completed his ophthalmology training at the New York Eye and Ear Infirmary, then completed two fellowships, cornea and external diseases at the Kellogg Eye Institute at the University of Michigan, and glaucoma at Bascom Palmer Eye Institute at the University of Miami. He joined Northwest Eye Surgeons in 2019.