American Board of Opticianry (ABO) Practice Test 2026 - Free ABO Practice Questions and Study Guide

Specific gravity is a measure that compares the density of a material to the density of water at a specified temperature. In the context of optometry, specific gravity is typically associated with the weight of optical materials, particularly lenses. Therefore, the correct answer focuses on the weight of a lens.

Understanding specific gravity is important when choosing lens materials, as it affects the overall weight and comfort of the glasses. Lighter lenses can improve patient comfort, particularly in eyewear that is worn for extended periods. The specific gravity influences how thick a lens needs to be for optical correction; in materials with higher specific gravity, a thicker lens may be necessary to achieve the desired prescription strength.

The other options may pertain to optical properties and characteristics of lenses but do not relate to the concept of specific gravity. Specific gravity does not directly measure brightness, thickness, or dispersion of light, which are separate attributes assessed through different metrics in optics. Thus, the focus on weight aligns correctly with the definition of specific gravity in the context of lens materials.