Which formulation is preferred to minimize ocular surface toxicity with chronic preserved drops?

• A. Preservative-free formulations.
• B. Higher concentration benzalkonium chloride.
• C. Alcohol-based preservatives.
• D. No solution.

Answer: (A)

Chronic preserved eye drops can irritate and damage the ocular surface because the preservatives, especially benzalkonium chloride, disrupt the tear film, stain and harm epithelial cells, and provoke inflammation with long-term use. Using preservative-free formulations removes this toxic exposure, so the ocular surface experiences less irritation, better tear film stability, and fewer signs of surface toxicity over time. This makes preservative-free options the better choice when drops are used chronically. The other options would either add more preservative, cause irritation, or provide no active medication at all, which defeats treatment goals.