A review of the practice-changing, myth-busting evidence
Yes, high-dose topical anesthetic damaged my cornea, but my eyes are more sensitive than yours.
Patients with corneal abrasions typically present to the emergency department with eye pain. Even though we use topical anesthetics to facilitate the exam, most physicians discharge these patients with just oral or topical NSAIDs and antibiotics. Under this regimen, the patient’s eye pain often worsens after leaving the ED and may not substantially improve for days.
Why don’t we write prescriptions for topical anesthetics upon discharge? And where did we get the evidence for this practice?
As it turns out, the evidence for the toxic effects of topical anesthetics comes from case reports, case series, and animal studies (See Table 1). For all but one of these cases. the patients were abusing topical anesthetics for weeks to months and/or with concentrations higher than that typically used today. So categorical statements that topical anesthetics have toxic effects on the cornea and decrease or inhibit corneal re-epithelialization may be more myth than reality since they result from cases involving patients abusing these medications – and/or not using them as prescribed (for short periods of time).
There also are two animal studies (Bisla and Tanelian 1992) and (Maurice and Singh 1985) that examined toxicity of topical anesthetics. In these studies, topical anesthetics were being used at increasing concentrations until corneal epithelial damage was seen. However, both studies were from the corneas of rabbits that have a more sensitive cornea and a reduced blinking rate when compared to humans. Therefore, it is hard to draw generalizations to humans.
A review of trials that have evaluated the use of topical anesthetics on corneal abrasions clearly demonstrates that topical anesthetics did a better job of controlling pain in all but one of the studies. There was no statistical difference in corneal epithelial healing observed at 72 hours (see Table 2).
It is important to ensure that your patient does not have a complicated corneal abrasion before discharge with topical anesthetics. A complicated corneal abrasion is defined as:
• 36 hours or more after initial injury
• < 18 years of age
• Patient wears contact lenses
• Injury to both eyes
• Grossly contaminated foreign body in eye
• Current herpes keratitis
• Allergy to tetracaine
• Injury requiring urgent ophthalmology evaluation
• Unable to make follow-up at 48 hours
Take Home Message
To date, the only evidence that topical anesthetics in uncomplicated corneal abrasions causing more harm than benefit come from experimental animal studies, case reports, and case series. Other studies showed superior pain control without delayed wound healing. Based on available evidence, it is most likely reasonable to send patients home with dilute (0.5%) topical anesthetics for a period of no more than 24 – 48 hours as long as these patients do not have complications. Larger, prospective studies would lend more weight to this recommendation.
More information can be found on www.rebelem.com, including:
• Historical case reports, case series, and animal studies (The dogma of topical anesthetics being unsafe for corneal abrasions)
• Other trials evaluating the safety and effectiveness of topical anesthetics
• My review of the Waldman et al study
• A summary of the commentary article that was released shortly after the Waldman et al publication
• How your pharmacist can make a 1:10 dilution of topical anesthetics
Salim Rezaie, MD is the founder and editor of REBEL EM.