A middle-aged female presents with a minimally injected right eye of one days duration. She says her eye has been very itchy, and she admits to rubbing it a lot. There is a mild punctate epitheliopathy that appears consistent with a mechanical abrasion from the rubbing. However, she seems to be in a disproportionate amount of discomfort relative to the condition. She is diagnosed with allergic conjunctivitis and prescribed a topical steroid and antihistamine.

She returns the next day reporting significantly more discomfort. Biomicroscopy reveals a greater amount of punctate epitheliopathy and a great increase in focal stromal edema. Inspection of past records reveals a history of non-descript recurrent epitheliopathy in her right eye only. She also has a large herpetic cold sore on her lip. She is now diagnosed with herpetic disciform keratitis. The topical steroid is continued, and Viroptic (trifluridine, Monarch Pharmaceutical) is prescribed prophylactically.

She returns the following day with 80% of her epithelium eroded. An atypical adverse reaction to Viroptic is suspected, and the medication is immediately substituted with oral acyclovir while the steroid is maintained. But, through the next several days, the patients cornea continues to worsen with profound epithelial erosion and subsequent stromal infiltration, despite discontinuation of all topical medications, the use of non-preserved tears and a bandage soft contact lens. With her cornea thinning and the condition worsening, the patient sees an ophthalmologist. However, despite the ophthalmologists best efforts,the patients cornea continues to deteriorate.

Curiously, the patient begins to alternate office visits between practitioners, presenting as an emergency in one office even though she has an appointment at the other. Despite everyones best efforts, her cornea fails to heal.

Finally, when all diagnostic options appear to have been exhausted, a curious finding is noted during one of the patients visits: There are no proparacaine bottles in the exam room. Upon direct confrontation, the patient admits to taking bottles from each office at every visit. This brings us to this months topic: the abuse of topical anesthetics.

Corneal Toxicity
Corneal toxicity to topical anesthetics is a well-known phenomenon. Punctate epitheliopathy from topical medication toxicity in another patient.1-11 The toxicity affects the cornea in several ways. Proparacaine, for instance, has toxic effects on stromal keratocytes that are related to drug concentrations and temporal exposure.12 Proparacaine also appears to inhibit corneal epithelial migration and adhesion. Epithelial cell spreading is completely abolished, and most cells detach from the substratum with prolonged use, leading to corneal non-healing.13 Abuse of topical anesthetics also appears to produce irreversible damage to the apical cell attachments at the level of the corneal endothelial cells.14

The mechanism of corneal damage on a clinical level is unclear. Most likely, the abuse of topical anesthetics leads to a self-induced neurotrophic keratitis. Neurotrophic keratitis is characterized by impaired healing of the corneal epithelium due to interrupted innervation.15,16 When ocular surface sensation is impaired, reflex tear secretion is reduced, yielding an aqueous tear deficiency. Trophic input to the corneal epithelial cells also appears to be reduced, decreasing mitotic activity and further compromising healing mechanisms. Data on the neurotransmitter and neuropeptide contents of corneal nerves indicate that they are integral players in the mechanisms by which corneal neurochemicals and associated neurotrophins modulate corneal physiology, homeostasis and wound healing.17

Punctate epitheliopathy from topical medication toxicity in another patient.

Abuse of topical anesthetics is difficult to diagnose, as it mimics several known conditions, namely Acanthamoeba keratitis, herpetic keratitis and fungal keratitis.3-5,8,9,18 In fact, abuse of topical anesthetics leaves the cornea vulnerable to secondary infection.2,5,19 One prominent finding in many cases of topical anesthetic abuse: the development of stromal ring infiltrates, hence the confusion with Acanthamoeba keratitis.1,3,4,6,7,9-11 Other findings include stromal scarring, epithelial sloughing, chronic non-healing of the epithelium and corneal perforation.1,3,4,6,7,9-11

Often, the diagnosis of topical anesthetic abuse is made ex juvantia (by exclusion) when all other treatments fail. This diagnosis is further complicated because patients often lie about abusing anestheticssomething to consider in the differential diagnosis of any keratitis that is unresponsive to treatment.20

Management involves the total discontinuation of topical anesthetics by the patient and copious use of artificial tears. A bandage contact lens may be necessary. Topical NSAIDs, such as Voltaren (diclofenac, Novartis Ophthalmics), have been used for pain management while discontinuing topical anesthetics.19 Corneal transplantation is often necessary.

Psychiatric counseling may also be warranted here. The reasons patients abuse topical anesthetics vary. Some may seek to quietly self-induce injury and then sue a doctor for malpractice. Others may suffer from Munchausen syndrome, in which the patient enjoys the attention associated with illness. Most likely, patients simply dont appreciate the potential harm and potency of simple eye drops.

We learned early on in optometry school that patients may steal topical anesthetics from an exam room in order to self-medicate. As this scenario illustrates, it does happen. So, create safeguards in your practice to limit patient access to high-hazard pharmaceuticals, such as proparacaine.

Drs. Sowka and Kabat are members of Alcons speakers alliance. They have no financial interest in any of the products mentioned.

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Vol. No: 143:03Issue: 3/15/2006