No Optometry school is going to invite every applicant for an interview. Schools interview students they think will be good for their program. The interview is used to make sure the applicant would be a good fit. If you've been invited for an interview, then you've made the cut on paper (most of the time). Do keep in mind though that schools interview more applicants than they have spaces available, because they know that not every acceptance letter they send out will mean a student in the upcoming class. You still need to be a competitive interviewer, but an interview invite is cause for rejoicing, so... good job.