As you might expect multiuse eye drops must contain a preservative in order to avoid contamination. The most common preservative, Benzalkonium chloride (BAK), has been around for over 50 years and is in most of our eye drops. In low concentrations it stops bacteria from multiplying, while in higher concentrations it kills them.

The rub: What is toxic to bacteria is also harmful to our sensitive ocular tissues. The more frequently drops are administered for conditions like glaucoma, dry eye, allergy, and conjunctivitis the more likely will our conjunctiva and cornea be irritated. Tears are made in the conjunctival goblet cells, the lachrymal glands, and the oil glands in the eyelids. Alteration of these tissues creates an unstable tear film. 

This means that the lubricating coat breaks up quickly and can actually reduce vision while causing redness. So if you notice increased burning, stinging, dryness, grittiness, redness, and even tearing consider that it may be related to your long term eye drops. Check the label to see if they are preserved with BAK. Be a medical detective and inform your doctor.

One of the main areas preservative toxicity may occur is glaucoma. Fortunately, there are three eye drops which offer an option: Travatan Z, brimonidine / Alphagan P and Timoptic in Occudose form. Glaucoma patients can also be considered for an Argon laser procedure to reduce the need for medication.

Therefore, it is wise to treat a condition quickly and then reduce or eliminate medication. It's also important to read the label on our eye drops because they are drugs. Preservative free artificial tears are available over the counter for dry eye patients; but first be certain that your eye drops have not induced your condition. It can be said that less is better.