it really depends on what u want to do but the truth is....
if ur really_ambitious and want to have doors open for u that would otherwise be very hard to get into (e.g. academic leadership positions in optometry), then by all means do MS/OD. (though u probably will need to get PhD to really have stuff open, e.g. President of OD school, Dean of Science faculty, Editor-in-Chief of optometry journals, being on the invited international lecturer circuit, being "famous" within optometry, etc.).
that said, going down research is a totally different career path that is almost certainly going to be less lucrative, and less certain than PP, in the long run.