Toxicities of topical ophthalmic anesthetics

Abstract

Topical ocular anesthesia has been part of ophthalmology for more than a century. The most commonly used drugs today are proparacaine, tetracaine, benoxinate (oxybuprocaine) cocaine and lidocaine. Although generally well tolerated, all these can be toxic, particularly when abused. The most common toxicities are to the ocular surface, but abuse can cause deep corneal infiltrates, ulceration and even perforation. Fortunately, systemic side effects are rare. Cocaine is unique for its higher incidence of systemic side effects and high abuse potential, both of which impede its clinical use. When used appropriately, all these drugs are remarkably safe. They are generally not prescribed for home use, as prolonged abuse of these drugs can be expected to result in serious complications.

Keratopathy due to ophthalmic drug abuse with corneal melting and perforation presenting as Mooren-like ulcer: A case report

“…Early corneal damage can be identified on the first day of topical application of an anesthetic, and is characterized as a smoothly structured periphery and a pitted corneal surface. If not treated or improperly treated for a number of days or weeks, infiltration in the corneal stroma may appear along the rims of the area of defected epithelium, forming a progressive ring lesion that can lead to corneal ulceration, thinning and eventually perforation and endophthalmitis (10,11). Prompt diagnosis is crucial, as patients typically continue to use topical anesthetics for pain management if no warning is given.…”

“…Topical anesthetics may paralyze corneal perception, reduce blink reflex and suppress reflex weeping. This increases the duration of exposure of the cornea to the air and promotes apoptosis (10), and therefore the ability of corneal epithelial cells to resist infection and foreign bodies is significantly reduced. In addition to initially compromising the integrity of the corneal epithelial barrier, topical anesthetics exert inhibitory effects on respiration, glucose metabolism and mitosis of corneal epithelial cells, disrupting the process of re-epithelialization (6,12,13).…”

Effect of topical anesthetic agents and ethanol on corneoepithelial wound healing in an ex vivo whole-globe porcine model

“…Such damage can be induced not only by mechanical injury but also by contact lens wear and by the topical application of anesthetic agents or ethanol. [1][2][3] Topical anesthetic agents are used in anterior segment surgery 4,5 and for postoperative analgesia after photorefractive keratectomy (PRK), 6,7 although their toxicity is under debate. 6,[8][9][10] Ethanol is used to create epithelial flaps in laser light-induced epithelial keratomileusis.…”

Study Design and Methodologies for Evaluation of Anti-glaucoma Drugs

“…The probe is so light (0.027 g) that it can be used to estimate IOP without the instillation of topical ocular anesthesia. This allows one to avoid this potentially confounding variable in topical anti-glaucoma drug studies [28]. Six individual measurements are obtained, internally averaged, and the IOP estimate is displayed accompanied by a letter indicating the species-specific calibration curve that was used.…”

“…Although generally well tolerated, topical proparacaine may transiently markedly reduce tear production (83 % in beagles in one study) [48], alter corneal thickness [49], corneal epithelial cell adhesion and the corneal penetration of topically applied drugs [50]. Recently, tetracaine was demonstrated to result in a decrease in IOP of 17-29 % for the first 20 min after its application in normotensive rabbits, and 24-31 % in rabbits with ocular hypertension induced by water loading [51].…”