Reviewed by Dr. Davinder Sidhu, OD
For those reading who are older and already using a preserved glaucoma drop every day, adding a preserved artificial tear on top is not recommended. As our eyes age with us, they produce less tear film to dilute what you put in, and older patients tend to use more drops per day, so the preservative builds up on the eye that's least able to clear it.
That's one of the main reasons why I recommend preservative-free as you age. It comes down to chemistry and tear volume, not marketing.
Older eyes carry more of the preservative load
Tear production reduces with age. By your seventies we make less of the watery part of our tears, blink is often weaker, and the tear film breaks up faster. All of that means a drop sits on the surface longer and gets diluted less than it would in a younger eye.
Older patients also often use more drops in a day and if managing other eye symptoms they could be using drops four to eight times before the sun goes down.
The preservative in question is usually benzalkonium chloride, or BAK. It's a detergent that keeps the bottle sterile after opening. For someone using a drop twice a week, that's not much of an issue. The problem is dose and frequency, and older patients tend to be high on both.
Glaucoma drops already deliver a daily dose of BAK
A lot of older adults are also on daily glaucoma drops, and many of those drops are preserved with BAK. Preservative-free artificial tears reduce the preservative load on the surface of the eye. They do not treat, control, or cure glaucoma. Your prescribed pressure-lowering drops do that, and you keep taking them exactly as your optometrist or ophthalmologist directed. What we're talking about here is only the drops you add on top.
When eyes feel dry or gritty, and preserved glaucoma drops are themselves linked to more surface irritation over time, the natural response is to reach for artificial tears. If those tears are also preserved, that's a second daily source of the same preservative on a surface that's already irritated.
A large European survey in 2007, covering around 9,000 glaucoma patients, found that patients on preservative-free drops reported fewer symptoms of irritation, burning, and dry-eye sensation than those using preserved formulations. BAK is toxic to the surface cells of the eye in a dose-dependent way, and the effect builds up with repeated exposure. Repeated exposure is exactly what an older patient on daily drops has.
A patient example
Here's a version of a patient I see fairly often. A woman in her late seventies, on a preserved glaucoma drop twice a day for years. She'd added a preserved artificial tear from the pharmacy, using it four or five times a day because her eyes burned, especially through the dry interior winter with the furnace running. The burning was getting worse, and she'd put it down to the glaucoma or just her age.
We left her glaucoma medication alone. We only changed the artificial tear, from preserved to preservative-free, and spaced it out from her pressure drop. A few weeks later the burning had settled down. Same eyes, same disease, but crucially one fewer source of preservative on the surface through the day.
Arthritic hands change which bottle actually works
Preservative-free used to mean single-use vials, the small plastic ampoules you twist open, use once, and throw out. They work in principle. In practice, they're hard for someone with arthritis, a tremor, or reduced grip strength. The vials are small and fiddly, and people end up squeezing half the vial onto their cheek or giving up and going back to the easy squeeze-bottle, which is usually the preserved one.
The alternative is a preservative-free multidose bottle. Same benefit of no BAK, but it's a normal bottle you pick up and squeeze, with a valve or filter tip that keeps it sterile. For an older patient, or a caregiver putting drops in for a parent, that difference often decides whether the routine actually gets followed.
I-Drop Pur is one I point a lot of older patients toward for everyday use. It's a preservative-free hyaluronic acid drop in a multidose bottle, so there's no vial to manage. When the surface is inflamed after years of drops, Thealoz Duo is worth considering, its trehalose helps protect the surface cells directly. Both are in our eye drops range.
What to do if you're stacking drops
Start by counting every drop that goes in your eye in a day, prescription and over-the-counter both. Discuss with your optometrist, if you're using preserved drops on cutting the preservative load.
Ask your optometrist or pharmacist whether your glaucoma drop comes in a preservative-free version, as many now do.
For the artificial tears you add yourself, there's no strong reason for those to be preserved if you're using them more than a couple of times a day. Move to preservative-free, ideally a multidose bottle you can open easily, and space your tears out from your pressure drops by five minutes or so.
The artificial-tear side isn't usually covered by a provincial drug plan the way a prescription might be, so it does come out of pocket. If you want the background on dry eye and surface health, the Canadian Association of Optometrists keeps a dry eye page that's worth reading.
For the full picture on making the switch, our complete guide to preservative-free eye drops covers where to start.
Younger eyes tolerate preservatives better. Older eyes tolerate them less, and older patients are more likely to already be carrying a daily preservative load from a prescription. That's why preservative-free is more of a senior issue than a general one.
About the Reviewer
Dr. Davinder Sidhu is an optometrist based in British Columbia with a focus on dry eye management and preservative-free solutions. Learn more at TheGenuwineOD.com or follow him on Instagram and Facebook.
