AIM: To evaluate the changes in central corneal thickness (CCF) caused by mydriasis with Mydrin-P.METHODS: A total of 106 eyes of 53 patients with refractive errors were studied. Each eye had instillation of Mydrin-P to obtain mydriasis. CCT was examined before and after mydriasis using ultrasonic pachymeter.RESULTS: CCT increased significantly after mydriasis with Mydrin-P.CONCLUSION: Mydrin-P can affect the measurement of CCT.