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Clinicopathologic Reports, Case Reports, and Small Case Series
May 2002

Unilateral Mydriasis Associated With Exposure to Flea Spray

Arch Ophthalmol. 2002;120(5):665. doi:

Anisocoria is a frequently encountered condition that often requires neurologic evaluation. Although it may occur with third nerve palsy, other causes include benign conditions, such as pharmacologic dilation, local iris sphincter abnormalities, tonic pupil, or sympathetic irritation.1 Unilateral miosis has been reported to result from exposure to cholinesterase inhibitors found in both flea foggers2 and pet flea and tick collars.3 We report a case of unilateral mydriasis associated with exposure to flea spray.

Report of a Case

A 3½-year-old boy was brought to the emergency department by his parents, who noticed that his pupils were of unequal size. There was no history of trauma, recent illness, medication use, or access to ophthalmic drops. Further inquiry revealed that the child had been playing with the family dog, which was recently treated with Sergeant's Flea and Tick Spray (Sergeant's Pet Care Products, Omaha, Neb). His behavior and activity had been normal. Vital signs were normal for his age, and results of a pediatrician's examination revealed no abnormalities other than anisocoria. Ophthalmologic examination results revealed a visual acuity of 20/30 OU using Allen figures at near. Anterior segments were normal when examined with a handheld light. Versions, alignment, and dilated fundus examination results were normal. There was no evidence of disc edema. Intraocular pressure readings were 13 mm Hg OD and 14 mm Hg OS. Under lighted conditions, the right pupil was 6.5 mm and the left pupil was 4 mm. In dim light, the right pupil measured 7 mm and the left pupil measured 5 mm. Both the direct and consensual pupillary light responses were 1+ OD and 3+ OS. The near response was also 3+ OS and 1+ OD. Results of computed tomography of the head performed without contrast showed no evidence of intracranial masses, edema, or dilated ventricles. The mydriasis and pupillary reactivity of the right eye had improved by the examination on the following day. Although the child failed to return for a subsequent examination, a telephone conversation with his mother revealed that the pupil inequality had resolved and that he was doing fine.


The active pesticide in Seargant's Flea and Tick Spray and related products permethrin is a type I pyrethroid. Pyrethroids have been found to produce potent sympathetic activation; local effects, such as paresthesia, have been reported with skin contamination.4 Additionally, α-adrenergic–mediated effects have been noted in animal studies using allethrin, another type I pyrethroid.5 We suggest that the patient's unilateral mydriasis may have been due to a local effect of permethrin that occurred after inadvertent rubbing of the eye following skin contamination. The local sympathetic effect did not alter near vision but produced mydriasis that was partially overcome by bright light and significantly improved the following day. To our knowledge, this is the first reported case of mydriasis occurring in association with exposure to flea pesticide products. It is important to consider exposure to pesticides during the evaluation of anisocoria since it may prevent costly and unnecessary imaging in the otherwise healthy patient.

None of the authors have any proprietary interests in the product mentioned in this article.

Corresponding author and reprints: Charlise A. Gunderson, MD, University of Texas Medical Branch, Department of Ophthalmology and Visual Sciences, 301 University Blvd, Galveston, TX 77555-0787 (e-mail: cgunders@utmb.edu).

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