American Board of Ophthalmology (ABO) Practice Exam

What percentage of light is reflected from a CR-39 lens surface?

1. 2%

2. 4%

3. 6%

4. 8%

The correct answer is: 4%

When considering the reflectivity of CR-39 lenses, which are a common type of plastic used in eyeglass lenses, the correct answer reflects the fact that approximately 4% of light is typically reflected from a single surface of a CR-39 lens. This is primarily due to the lens material's refractive index and surface characteristics, which determine how much light can be reflected rather than transmitted through the lens. Understanding the optical properties of materials such as CR-39 is crucial for selecting the right lens for patients, as reflection can impact both the aesthetics and functional performance of the eyewear. In practice, this means that for every surface of the lens, a notable percentage of light will not reach the eye but will instead be reflected away. This knowledge is particularly important when considering lens coatings that could minimize reflections and enhance visual clarity. In summary, the reflectivity of 4% from a CR-39 lens surface is an important characteristic to consider when discussing optical performance and patient comfort.