Allergic and toxic reactions of soft contact lens wearers

The allergic and toxic effects of preservatives found in soft contact lens solutions are reviewed. Thimerosal, a preservative commonly found in soft contact lens solutions, may cause ocular delayed hypersensitivity. Patients with delayed hypersensitivity to thimerosal may develop conjunctival hyperemia, corneal infiltrates and intolerance to lens wear with the use of soft contact lens solutions containing thimerosal. Delayed hypersensitivity to thimerosal can be demonstrated by an occlusive patch test or intradermal injection. Discontinuation of chemical disinfection with substitution of thermal disinfection using unit-dose, non-preserved saline causes resolution of signs and symptoms. Another cause of lens wear intolerance is contact lens-associated giant papillary conjunctivitis. Protein deposits on the lens may act as antigens and initiate an allergic condition which disappears when the lens is discontinued. Alternatively, the giant papillae may be the result of mechanical irritation induced by the contact lenses. The chemical preservatives that are found in soft contact lens solutions cause epithelial toxicity when applied to isolated rabbit corneas. However, corneal toxicity toxicity in a clinical setting has not been demonstrated.