Milkweed Corneal Toxicity
Plants in the Asclepias family, known colloquially as “Milkweed” plants due to their milky sap, are commonly found in household gardens because of their colorful, ornate, flowers and role in the lifecycle of monarch butterflies. Unsuspecting gardeners and children have been known to touch the sap, called latex, and suffer from toxic side effects. Contact with ocular structures leads to an inflammatory response with concurrent corneal edema.
Milkweed plants produce Carnenolides, which are cardiac glycosides akin to Digitalis capable of binding to Sodium/Potassium ATPases (Na+/K+-ATPases). As a result, direct ocular exposure can inhibit corneal pump function with resultant corneal edema and ocular irritation.
Diagnosis of Milkweed corneal toxicity is clinical. Patients, particularly children, may or may not make the connection between plant exposure and onset of symptoms. Thus, a high index of suspicion is needed when obtaining a history and examining patients. The clinical exam is defined by conjunctival injection, corneal edema, and Descemet folds. Intra-ocular pressure is typically normal. Signs of severe ocular toxicity such as perilimbal whitening, anterior uveitis, and symblepharon are not typical.
One must consider any condition that can cause corneal edema and conjunctival injection:
- Viral Conjunctivitis
- Herpes keratitis
- Acid or Base Related Chemical Keratitis
- Acute Angle Closure Glaucoma
- Anterior Uveitis
Like any ophthalmic chemical exposure, removing the offending agent and ensuring anterior segment stabilization is important. Prompt ocular irrigation with saline solution and measurement of ocular pH is advisable. Interestingly, in-vitro studies have demonstrated a direct benefit to treatment with topical dexamethasone as it is able to up-regulate Na+/K+-ATPase activity in the corneal endothelium and expedite corneal recovery. Concurrent use of a hypertonic agent, such as 5% sodium chloride, can also decrease corneal edema via an osmotic effect. Patient should be monitored closely with daily exams until clinically stabilized. Fortunately, most patients recover in a matter of days with no residual sequela.
Milkweed exposure is an important clinical entity that causes significant ocular toxicity that, with appropriate anterior segment stabilization and topical steroids/osmotic agents, can be managed effectively by eye providers. A high index of suspicion is needed to make this diagnosis and clinicians should be careful to exclude more common, vision-threatening etiologies.
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