The Dry Eye Zone

Rebecca's Blog

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Study: Preserved versus unpreserved artificial tears

Of preservatives, vices and virtues

If you’re reading too quickly and looking for a really short soundbite, you may come away thinking the opposite of what I mean. How do I know? Because of how many times I’ve written about this before.

Here is something I have tried to explain time out of mind about preservative-free artificial tears:

“Preservative-free” is not a virtue. It’s simply the absence of a vice.

In other words, just because an eye drop has no preservatives doesn’t mean it’s any good. Absence of preservatives don’t make an eye drop WORK better. It just means it doesn’t contain a preservative, so you won’t have any side effects that might be associated with the particular preservative it contains.

An artificial tear can be preservative-free and useless, or preservative-free and ineffective for you, or even preservative-free and uncomfortable for you, knowing how individual our responses to eye drops tend to be.

Conventional wisdom says to use preservative-free eye drops if you are using eye drops frequently and/or have a sensitivity. But once you’ve learned to read the labels and find the preservative-free ones, you still have to find something that “works”, i.e. that achieves your goals - that gives you more comfortable eyes or eyes feeling a particular way for long enough to be worth it.

A study asking if preservative-free tears work better

The following “systematic review” type study evaluated efficacy of preserved versus unpreserved artificial tears in medical literature in the past umpteen years, and basically answered that there’s no meaningful evidence out there that preservative-free artificial tears work better.

There are a number of unsurprising but objectively remarkable things about this study. For example, in so many years of studies, how is it that only FOUR studies were relevant to the research question? Is it because no one cares enough to properly research the efficacy of over-the-counter eyedrops, other than, say, their own manufacturers? Is it because of a total lack of consistency in the yardstick used to measure efficacy in these studies - or maybe even in therapeutics for dry eye disease in general? To all of which my personal answer would be, YES.

Then there’s a more troubling question. Apparently this study also looked at safety questions. But if so, how could they fail to find a track record of side effects from preserved eye drops? Which preservatives were in the drops in the studies they identified?

Does anybody ever study the effects of preservatives in anything other than, say, glaucoma medications? If not, why not?

More research, please.

And the abstract at last…,

Effectiveness of using preservative-free artificial tears versus preserved lubricants for the treatment of dry eyes: a systematic review. Ribeiro et al, Arq Bras Oftalmol. 2019 Sep 9;82(5):436-445.

This systematic review aimed to assess the effectiveness of using preservative-free artificial tears versus preserved lubricants for the treatment of dry eyes in Universidade Federal de Alagoas (PROSPERO 2018 CRD42018089933). Online databases were searched (LILACS, EMBASE, MEDLINE, and CENTRAL) from inception to April 2018; references from included papers were also searched. The following keywords were used: lubricants OR artificial tears OR artificial tears, lubricants AND dry eye OR dry eye syndrome OR syndromes, dry eye OR dry eyes. Among the 2028 electronic search results, 29 full papers were retrieved and four were considered relevant. The number of participants from these studies ranged from 15 to 76. Meta-analysis was possible for the following outcomes: score of symptoms according to the Ocular Surface Disease Index - Allergan (OSDI), tear secretion rate using the Schirmer test, tear evaporation rate using the tear film breakup time test, burning, foreign body sensation, and photophobia. No statistically significant difference was observed between the two groups, and no side effects were attributed to the interventions. Evidence proving that preservative-free artificial tears are more effective than preserved artificial tears is lacking.