Reference Letters

Hi guys! I'm a 3rd year undergrad student and I am planning on writing my OAT this summer (2015) and also applying at the end of August. If I don't get accepted anywhere for 2016, I was thinking of doing a year of research after completing 4th year and applying again for 2017. So basically, my question is, can I use the same reference letters from the Optometrist and Optician at the clinic I worked at the second time I apply or will I have to ask them to write me new reference letters? Which...

Reference Letters