Effects on pupil size and accommodation from topical lidocaine hydrochloride and tetracaine hydrochloride

The aim of this study was to quantify the mydriatic and cycloplegic effects from topically applied lidocaine hydrochloride 4% and tetracaine hydrochloride 1% in healthy volunteers.

Twenty-six (26) healthy volunteers age 23 +/- 2.5 years were included in this double-masked, randomized, intraindividually comparing study. All participants were given a drop of lidocaine 4% in 1 eye and tetracaine 1% in the contralateral eye three times with a 90-sec interval, which was subject to randomization. Before the eye drops, and 15, 30, 45, 60, 90, and 120 min after the application of the last drop, Scheimpflug photography was performed in each eye, and the near point was determined using a near-point ruler. Before the eye drops and at 60 and 120 min, the visual acuity was determined with the ETDRS chart. The extent and time course of the mydriatic and cycloplegic responses were determined.

Significant pupil dilation was seen with both substances; an increase from 3.25 +/- 0.48 to 3.52 +/- 0.76 mm (8.8 +/- 3.9%; P = 0.036) at 30 min with lidocaine, and from 3.19 +/- 0.46 to 3.44 +/- 0.49 mm (8.8 +/- 2.9%; P = 0.008) at 45 min with tetracaine. A subgroup analysis revealed that a mydriatic effect could only be detected in eyes with pale irides (P < 0.01). In pigmented irides, a slight miotic effect was noted. A decrease in accommodation was also seen: from 9.8 +/- 1.6 to 9.1 +/- 1.7 D (6.3 +/- 2.9%) at 15 min with lidocaine, and from 9.7 +/- 1.4 to 8.8 +/- 1.5 D (7.8 +/- 3.7%) at 30 min with tetracaine. Again, the effect was more pronounced in pale irides (P < 0.05). Both substances induced a small increase in corneal thickness (P < 0.01). A substantial epithelial opacification was noted with tetracaine, but not with lidocaine.

Lidocaine 4% and tetracaine 1% exhibit significant mydriatic effects upon topical administration in eyes with pale irides. The mydriatic effect is more rapid and prolonged with lidocaine than with tetracaine.