SGEM#315: Comfortably Numb with Topical Tetracaine for Corneal Abrasions

Date: January 5th, 2021 Reference: Shipman et al. Short-Term Topical Tetracaine Is Highly Efficacious for the Treatment of Pain Caused by Corneal Abrasions: A Double-Blind, Randomized Clinical Trial. Annals of EM 2020 Dr. Glaucomflecken Guest Skeptic: Dr. Will Flanary is an ophthalmologist, writer, and comedian who moonlights in his free time as “Dr. Glaucomflecken” on Twitter and TikTok. Effortlessly blending humor with education, Dr. Glaucomflecken has spent the last five years informing audiences on a wide range of topics, like navigating the confusing world of over-the-counter eyedrops, the horrifying consequences of sleeping in contact lenses, and his recent experiences as a patient in the medical system. Case: A 32-year-old healthy man presents with left eye pain. He was giving his 9-month-old a hug and got poked in the eye with a sharp little fingernail.  His visual acuity is 20/20 bilaterally and he doesn’t wear corrective lenses or contact lenses. He tried some over-the-counter red eye drops that did not seem to work. In the emergency department (ED), tetracaine drops are applied prior to slit lamp examination and the pain is completely resolved. On examination, you see a vertical corneal abrasion with no evidence of ulceration and no foreign body. You prescribe antibiotic drop and prepare to discharge him home when he asks, “can I get some of those numbing drops to use at home”? Background: Even small corneal abrasions can cause significant pain because the cornea is highly innervated. The first documented use of topical ophthalmologic anesthetics was in 1818. A cocaine derivative was employed to effectively block nerve conduction in the superficial cornea and conjunctiva (Rosenwasser). A number of proposed dangers have limited the use of topical anesthetic agents for the treatment of corneal abrasion associated pain. These dangers include delayed healing secondary to mitosis inhibition and decreased corneal sensation. The latter issue is of concern because of the potential for the abrasion to progress to an ulcer without the patient noticing. Additionally, these agents may have direct toxicity to corneal epithelium with prolonged use, leading to increased corneal thickness, opacification, stromal infiltration, and epithelial defects. The fear of these complications has led to the pervasive teaching that topical anesthetics should never be used for outpatient management of corneal abrasions. This is reflected in the condemnation of their use in major Emergency Medicine textbooks, including Rosen’s and Tintinalli’s. Some of the evidence used to support the claim of local anesthetics causing corneal harm comes from case reports, animal models or local anesthetic injected directly into the anterior chamber of the eye for cataract surgery. More information on the where the no topical anesthetic use on corneal abrasions come from can be found on a REBEL EM blog post. We covered and randomized control trial by Waldman et al on topical tetracaine for simple corneal abrasions on SGEM#83. The bottom line from that episode was that tetracaine appears safe for uncomplicated corneal abrasions and provides more effective pain relief than saline eye drops. We also did a critical appraisal of a systematic review by Swaminathan et al looking at topical anesthetics for these types eye injuries on SGEM#145. The SGEM bottom line from that review was that the best evidence we currently have demonstrates that dilute topical anesthetic drops of either proparacaine or tetracaine are safe for use in ED patients with simple corneal abrasions to provide analgesia. The studies are small, but the data contained in them is far superior to the case series published 50 years ago which led to the dogma that using them is dangerous. Clinical Question: What is the efficacy of topical tetracaine in the treatment of simple corneal abrasions? Reference: Shipman et al.