American Board of Ophthalmology (ABO) Practice Exam

Which optical property is crucial in determining the quality of a lens?

1. Thickness

2. Curvature

3. Index of refraction

4. Surface finish

The correct answer is: Index of refraction

The index of refraction is a central optical property that plays a significant role in determining the quality of a lens. It quantifies how much light slows down and bends when passing through a material compared to its speed in a vacuum. A higher index of refraction typically means that light will bend more significantly as it passes through the lens, allowing for thinner lens designs while maintaining the same focal length. This property directly affects the lens's ability to focus light accurately, impacting overall image quality and clarity. The index of refraction helps in minimizing optical aberrations, which can arise from the shape and material properties of the lens. By selecting materials with appropriate refractive indices, lens designers can optimize performance, leading to lenses that provide sharper images with reduced distortion. While thickness, curvature, and surface finish all contribute to a lens's quality, they influence the practical aspects of lens design and performance secondary to the foundational role that the index of refraction plays in determining how light interacts with the lens material itself. Thus, understanding the index of refraction is essential for predicting how effectively a lens will meet optical requirements.