Although you guys are giving great advise to this inquirer, I disagree on this point. Good OAT scores cannot entirely make up for a weaker GPA. While the OAT is a standard measure of a students academic ability, a GPA reflects how a student can manage many things at once (a difficult course load, extracurriculars, social activities, etc.). With this view, a GPA is a measure of how a student will be able to meet the demands as a busy and well-rounded optometry student and future optometrist.
However, I think getting high scores on the OAT to balance a lower GPA will show admissions committees that you are serious about pursuing optometry, and are willing to "step up your game" from your undergrad experience.
Just don't think that high OAT score will save you. Admissions committees generally look at everything about an applicant. Good luck with school, OAT's and future admissions!