OBJECTIVE To compare the degree and duration of corneal anesthesia of a novel viscous ophthalmic lidocaine hydrochloride preparation vs. two commonly used ophthalmic anesthetic preparations. METHODS Each subject was randomly selected to receive 2 of 4 treatments at 2 different time periods separated by a 1 week washout: 3.5% lidocaine hydrochloride gel (Akten® ; Akorn Inc., Lake Forest, Illinois, USA), 0.5% aqueous proparacaine hydrochloride (Akorn Inc.), 0.5% viscous tetracaine hydrochloride (TetraVisc™; Ocusoft Inc., Richmond, Texas, USA), or 0.9% saline eyewash as a negative control. Corneal sensitivity was determined using a Cochet-Bonnet aesthesiometer (LuneauÂ® , Chartres Cedex, France) prior to instillation of each treatment; at 1 and 5 min post treatment; and at 5-min intervals thereafter for 90 min total. Ocular side effects were recorded on a scale of 0-3. RESULTS Twenty-four normal dogs (48 eyes) were entered into the study. Mean duration of maximal anesthesia was significantly greater at 34.2 min with tetracaine compared to 21.5 min and 19 min with proparacaine and lidocaine respectively. Corneal sensitivity was significantly decreased from baseline for up to 70 min with tetracaine and 55 min with both proparacaine and lidocaine. All lidocaine-treated eyes had transient blepharospasm and conjunctival hyperemia. Ten out of 24 tetracaine-treated eyes had conjunctival hyperemia with 4 of these having concurrent chemosis. CONCLUSIONS Tetracaine provided a significantly longer duration of corneal anesthesia than proparacaine or lidocaine. Tetracaine and lidocaine were associated with more ocular side effects than proparacaine, although these were mild and transient. None.