Which preservative is linked to SLK?

• A. Benzalkonium chloride
• B. Thimerosal
• C. Chlorhexidine
• D. Sodium perborate

Answer: (B)

Preservative-induced ocular surface inflammation can contribute to superior limbic keratoconjunctivitis (SLK). Thimerosal is a mercury-containing preservative known to provoke allergic conjunctivitis and chronic irritation of the ocular surface. When used chronically in eye drops, it can incite inflammation concentrated at the superior bulbar conjunctiva and limbus, where SLK features such as lid-induced friction and conjunctival hyperemia are most apparent. This toxic or hypersensitivity reaction best matches the pattern seen in SLK, making thimerosal the preservative most linked to this condition. Benzalkonium chloride, chlorhexidine, and sodium perborate can cause ocular surface irritation as well, but their association with SLK is less specific or direct compared to thimerosal in practice.