The effect of corneal hypesthesia on the duration of proparacaine anesthetic eyedrops.

The duration of action of proparacaine is known in the normal cornea but not in the hypesthetic cornea. To determine this, we examined both eyes in seven patients with documented unilateral corneal hypesthesia associated with inactive herpetic disease. Cochet-Bonnet measurements were made in both eyes before and at two- to five-minute intervals after the instillation of one drop of 0.5% proparacaine until baseline corneal sensitivity levels were again achieved. Mean recovery time was 34.86 minutes in eyes with normal corneal sensitivity, compared to 45.43 minutes in hypesthetic corneas. In all patients, the recovery time was remarkably longer in the hypesthetic eye than it was in the normal fellow eye. These data demonstrate the need to wait up to one hour after the instillation of proparacaine in eyes suspected of having corneal hypesthesia if corneal sensitivity is to be determined accurately. Additionally, the duration of action of topically instilled anesthetic may be a useful method of discovering subtle differences in corneal sensitivity.