Generally speaking, when people are in their adolescence, their pupillary distance will change with their age. But once becoming an adult, a person's pupillary distance will not change any more. Not like prescription which may change owing to various factors, pupillary distance of adults will always remains the same. If you are an adult, and you have your pupillary distance measured recently again, but you find it different with the number that your pupillary distance used to be, the probable reason is the error in measurement. For more information about pupillary distance such as how to measure a person's pupillary distance, you can refer to the following web site.