American Board of Opticianry (ABO) Practice Test

How can plus lenses be characterized?

1. the radius of curvature of a one diopter lens

2. simple myopia or nearsightedness can be corrected with these type of lenses

3. plus spheres are used for farsightedness

4. converging/against motion

The correct answer is: converging/against motion

Plus lenses can be characterized as converging lenses, meaning they bend light rays towards a single focal point. This convergence occurs because plus lenses are thicker in the center and thinner at the edges, which effectively causes parallel rays of light to come together after passing through the lens. This property is crucial in correcting hyperopia (farsightedness), where the light entering the eye does not converge quickly enough before reaching the retina. The identification of plus lenses as having "against motion" in the context of lens testing is also important. When viewing an object through a plus lens, moving the lens away from the eye will cause the object to appear to move in the opposite direction, providing a practical means of assessing lens power during examination. In summary, recognizing plus lenses as converging lenses with their distinct motion characteristics is key in understanding their application in optical prescriptions, particularly for individuals with hyperopia.