accommodative convergence: accommodation ratio

ac·com·mo·da·tive con·ver·gence: ac·com·mo·da·tion ra·ti·o

(AC:A) (ă-kom'ŏ-dā'tiv kŏn-vĕr'jĕns ă-kom'ŏ-dā'shŭn rā'shē-ō) The amount of convergence (measured in prism diopters of convergence) divided by the amount of accommodation (measured in diopters) required to direct both eyes on an object.