Wednesday, 21 May 2014

Corneal abrasion? Yes you can take that topical anesthetic home!


For over twenty years I have heard that you can’t let patients go home with topical anaesthetic drops for treatment of their corneal abrasions. The fear is that this would somehow delay wound healing and their eyeballs would spontaneously combust and melt away.

Therefore I was more than pleased to see this double-blind randomized clinical trial conducted in an actual Emergency Department. Is undiluted topical tetracaine safe for the treatment of pain caused by corneal abrasions?

The lead author Dr Neil Waldman FACEM is to be absolutely congratulated for this undertaking. This trial was conducted in shiver-me-bones Invercargill, New Zealand. Anybody who is up on their geography knows this smaller regional community is located closer to Antarctica than anywhere else.  Conducting high quality research outside of a major tertiary centre is always challenging. It is quite clear that a lot of personal time, energy and effort went in to pulling this off.

The hypothesis of the study was that undiluted topical tetracaine would be safe for patients with corneal abrasions to use for 24 hours. Inclusion criteria were corneal abrasions, ultraviolet keratitis, and post foreign body removal (i.e. rust rings). Patients were randomised to tetracaine or saline and all got topical chloramphenicol ointment. The primary outcome measure was “safety” as measured by persistent fluorescein uptake of the abrasion at 48 hours and the occurrence rates of any prespecified complications. Secondary outcomes looked a reduced pain on a self reported VAS and an overall effectiveness score.

The results? 116 patients were included in the study. The conclusion was that topical tetracaine used for 24 hours is safe; the VAS pain score showed no difference but patient surveys on overall effectiveness showed patients happier with the tetracaine.

There is no such thing as a perfect study and to be honest, this one was a little sloppy. One would need to recruit many more patients than 116 in order to make any claims about safety. In fact, it is usually not feasible to conduct an RCT with a primary outcome of safety in mind. RCT’s usually focus on efficacy whereas large cohort studies have the statistical power to make claims about safety. So it is not surprising to see a confidence interval of up to 6.1% for this primary outcome.

There were a few other issues. The power calculation was backwards and not really followed anyway. The blinding was not that good, patients were lost to follow up, rust rings were a confounder, the self reported VAS was probably not an accurate measuring tool and the title is a bit misleading.

Despite off of this, I really like this paper. The literature search included in the discussion could not find any good quality evidence of harm in previous studies.  I like the conclusion of this paper and it will very likely change my practice. I am happily going to send patients home with corneal abrasions and some drops of topical anaesthetic.  It goes to show that important & meaningful clinical research can be conducted in smaller centres without much support. Well done!

Covering:

Waldman N, Denise IK, Herbison, P. Topical Tetracaine Used for 24 Hours is Safe and Rated Highly Effective by Patients for the Treatment of Pain Caused by Corneal Abrasions: A Double-blind, Randomized Clinical Trial. Acad Emerg Med 2014;21:374-382.

http://www.ncbi.nlm.nih.gov/pubmed/24730399
 

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