The Optometry Admission Test (OAT) is a standardized exam designed to assess competencies in areas important for success in optometry school and a career as an optometrist. The exam covers four content areas: Survey of the Natural Sciences (Biology, General Chemistry, and Organic Chemistry), Reading Comprehension, Physics, and Quantitative Reasoning.
You should prepare intensively by reviewing material in OAT prep books and taking repeated practice OAT exam. The OAT is generally taken in the late spring or early summer between your junior and senior year in college.
For more information, visit the Association of Schools and Colleges of Optometry's OAT page.