Investigating the effect of lidocaine on tropicamide-induced mydriasis

Objectives: To investigate if pre-instillation of 2% Lidocaine has a potentiating effect on pupillary dilatation and the time it takes to achieve the maximum pupil size with 1% tropicamide-induced mydriasis. Materials and Methods: A randomized study was carried out on one hundred and twenty subjects who had dark brown irides with no systemic or ocular disorders. They were randomly selected from a screening exercise among the southern Nigerian population. Horizontal Pupil diameter was measured and recorded using a ruled pupillometer, at baseline and every ten minutes post-instillation. The right eye received a drop of 2% lidocaine, masked and labelled as ‘eyedrop A’ while the left eye received a drop of 10mg/ml Benzyl Alcohol, masked and labelled as ‘eyedrop B’ which was used as a form of placebo. 3-minutes later, a drop of 1% tropicamide masked and labelled as ‘eyedrop C’ was instilled into each eye until clinically effective diameter (CED) and maximum dilatation were observed in the right and left eyes. Results: There was a statistically significant difference (p=0.000) in the mean horizontal pupil diameter of the right eyes compared to the left eyes. Meanhorizontal pupil diameter increased by 4.00 ± 0.14 mmin the right eye and by 2.77 ± 0.11mm in the left eye.100% of right eyes attained the CED of 6 mm while 90% of the left eyes attained CED of 6 mm. CED was achieved after 30 minutes in the left eyes compared to 20 minutes in the right eyes, a mean difference of 10 minutes which was statistically significant (p=0.000) .The time to achieve maximum pupil size was faster in the right eye. Conclusion: Pre-instillation of 2% lidocaine facilitates the mydriatic effect of 1% tropicamide in black irides. Keywords: 2% lidocaine, 1% tropicamide, black irides, mydriasis