Effects of the Cycloplegic, Cyclopentolate, on Measurements of Refraction in Eyes of a Strain of Wild-Type Juvenile Guinea Pig (Cavia porcellus): A Comparative Study

Objective: To investigate the effect(s) of the cycloplegic, cyclopentolate, on measurements of refraction in eyes of a strain of wild-type guinea pig.Methods: Both eyes of 13 wild-type juvenile guinea pigs (n = 26 eyes) were examined both pre- and post-mydriasis, using streak retinoscopy (SR) and eccentric infrared photoretinoscopy (EIP). On the day of measurement, three SR measurements were taken for each eye at 0900, 1000, 1100, 1400, 1500 and 1600, and three EIP measurements for each eye at 0930, 1030, 1130, 1430, 1530 and 1630. Cyclopentolate hydrochloride (1%) was topically administered three times to each eye at 5-min intervals: 1300, 1305 and 1310.Results: Repeated measurements made by either method revealed that mydriasis did not significantly affect refractive stability (repeated measures, p > 0.05). Depending on the stage of mydriasis, however, there were significant differences in measured refractive changes both SR and EIP (0.27 ± 0.65 D, tSR = −2.095, PSR = 0.04 and 0.73 ± 1.06 D, tEIP = −3.494, PEIP = 0.002, respectively) measurements.Conclusions: Cyclopentolate had only limited effects on measurements of refraction, indicating that direct SR or EIP measurements of refraction in this wild-type strain of juvenile guinea pig, without the use of a cycloplegic, yield reliable and stable results.