Which topical antiviral is associated with ocular surface toxicity with prolonged use?

• A. Acyclovir
• B. Ganciclovir
• C. Trifluridine
• D. Idoxuridine

Answer: (C)

Prolonged exposure of the ocular surface to a topical antiviral can irritate and damage the corneal epithelium. Trifluridine is a thymidine analog used to treat herpes simplex virus infections on the cornea, but it has a narrow therapeutic window and notable toxicity with extended use. Its effect on rapidly dividing corneal epithelial cells leads to signs like conjunctival irritation, tearing, punctate keratitis, and epithelial defects. Because of this, clinicians aim to limit how long trifluridine is used and monitor the eye closely, often switching to a less toxic option for longer treatment.

Acyclovir topical tends to be better tolerated on the ocular surface and is used for epithelial keratitis with fewer long-term toxicity concerns. Ganciclovir gel can cause some irritation but is generally well tolerated for longer courses. Idoxuridine is older and is known for substantial ocular surface toxicity and phototoxicity, so it’s used much less today.