Effect of topical anaesthesia on corneal epithelial fragility

The effect of topical anaesthetics on human corneal integrity was assessed by measurement of the alterations they cause in corneal damage threshold. The anaesthetics investigated were 1.0% Amethocaine HCl, assessed immediately after instillation and after delays of 20 min and 60 min, and 0.5% Amethocaine HCl and 0.4% Benoxinate HCl, assessed 20 min after instillation. At 20 min after instillation of 1.0% Amethocaine HCl, the corneal damage threshold was significantly decreased. At other times for this anaesthetic, and for 0.5% Amethocaine HCl and 0.4% Benoxinate HCl, the corneal damage threshold was unaltered.