American Board of Opticianry (ABO) Practice Test 2025 - Free ABO Practice Questions and Study Guide

A plus lens that, when moved from its primary position, results in a base-up (BU) prism effect is accurately described by the concept of decentering the lens. When a plus lens is decentered downward relative to the optical center, it creates a prismatic effect where light is bent upwards, leading to a BU prism effect. This phenomenon is essential in optometry and optical prescriptions since it demonstrates how the position of a lens can influence the perception and direction of light and how it is focused on the retina.

In contrast, other terms like "BI prism" or "BU prism" refer to specific configurations or types of prism effects rather than describing the action of decentering a lens. Additionally, a “press-on prism” typically refers to a prism that is temporarily attached to eyewear to provide a prismatic effect without modifying the lens alignment. Therefore, understanding the concept of lens decentering is crucial for managing and correcting vision accurately in patients.