Duration of Mydriasis Produced by 0.5% and 1% Tropicamide in Sprague-Dawley Rats

Ophthalmic examination (OE) is a common part of preclinical studies. Pupillary dilation to facilitate OE may affect results of other planned testing. The purpose of this study was to determine the duration of mydriasis produced by commercially available 0.5% and 1% tropicamide in ophthalmologically normal albino rats. Twelve female Sprague-Dawley rats were used. A single drop of 1% tropicamide was applied to one eye of each rat. A single drop of balanced salt solution (BSS) was applied to the contralateral eye. Measurements of pupillary diameter (PD) were obtained using a digital caliper at 0, 20, 40, 60, 120, 180, 240, 300, and 360 min after application. After a 3-wk washout period, the procedure was repeated using 0.5% tropicamide. Pupillary dilation sufficient to allow posterior segment evaluation was achieved with 0.5% and 1% tropicamide. Maximum PD after treatment with 0.5% tropicamide was 4.17 ± 0.22 mm at 40 min; maximum PD after treatment with 1% tropicamide was not significantly different (4.28 mm at both 20 and 40 min (±0.43 mm and 0.23 mm, respectively)). Mean PD remained above 3.5 mm in treated eyes for 60 min. In eyes treated with 0.5% tropicamide, mean PD was significantly different from baseline mean PD for that eye up to 300 min. In eyes treated with 1% tropicamide, mean PD was significantly different than baseline mean PD for that eye at all timepoints. Both concentrations of tropicamide produced a transient mild to moderate mydriasis in the contralateral eye. Duration of action is at least 5 h for 0.5% tropicamide and 6 h for 1% tropicamide. Results of this study support use of 0.5% tropicamide for OE in albino rats, with administration performed no more than 60 min prior to examination.