I have extremely bad hay fever. Oral antihistamines are insufficient, so I have been using Opticrom eyedrops, which are very effective. The instructions for these drops say they should not be used with soft contact lenses, which I wear. However, I was told that the warning was due to chemicals being absorbed by the lenses and damaging them, and that since the lenses are daily disposables, this was not an issue. I have recently learned that benzalkonium chloride, used as a preservative in Opticrom, is absorbed by the lens and is very toxic to the cornea. Am I likely to have done permanent damage to my eyes?

Paul

Preservatives such as benzalkonium chloride are a crucial ingredient in eyedrops because they help prevent infection. Many people touch the tips of eyedrop bottles to their eyes when they instill a drop. This contact allows bacteria from the skin to contaminate medicated eyedrops. When the eyedrops are used again, bacteria can be instilled in the eye along with the eyedrop. Fortunately, preservatives serve to kill bacteria.

There are many types of eyedrop preservatives, some more powerful than others. Manufacturers decide the strength of the preservative depending on the type of medication and how long they think the eyedrop might stay on a patient's shelf. For example, anti-allergy medications may be used a few times, and then stored for many months. On the other hand, glaucoma treatments must be used every day, so a bottle of eyedrops is usually finished in a matter of weeks.

Benzalkonium chloride is a strong preservative used in many brands of eyedrops that are usually stored for extended periods of time. The down side of benzalkonium chloride is that multiple exposures during the day can cause corneal irritation and toxicity. Patients should use drops preserved with benzalkonium chloride no more than four times a day. Even this level of exposure for multiple days can cause eye irritation.

As you mention, contact lenses add a different dimension to the toxicity issue. Benzalkonium chloride can be absorbed by the contact lens, and then slowly released over the course of the day. For people who use a particular contact lens for a week or two, the level of benzalkonium chloride in the contact can get high, and continued wear can lead to moderate to severe eye irritation. Even people with daily-wear contact lenses (contact lenses that are thrown away each night) should try to avoid drops with benzalkonium chloride.

For people who require multiple eyedrops during the day, there are a few options. The first is to wear eyeglasses instead of contacts for the few days to weeks that the eyedrops are required. Another is to have your doctor prescribe a medication that only requires two applications a day (once in the morning before the contact lenses are used, and once in the evening after the lenses are removed). If that's not possible, discuss with your doctor the possibility of using Opticrom only twice a day rather than the usual four-times-per-day dosage.

As for your question about permanent damage, the eye irritation caused by benzalkonium chloride and other preservatives usually goes away once the exposure to the preservative is discontinued.