American Board of Ophthalmology (ABO) Practice Exam

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Which index is generally standard for lens manufacture in the US?

1.48
1.50
1.53
1.55

The correct answer is: 1.53

The index that is generally standard for lens manufacture in the US is 1.53. This refractive index is significant because it offers a good balance between thinness, weight, and optical clarity, making it suitable for a wide range of lens prescriptions. Lenses with a refractive index of 1.53 are considered mid-index lenses and provide improved comfort and aesthetics compared to standard plastic lenses, which typically have a refractive index of around 1.49. Moreover, lenses at this refractive index are commonly used in progressive addition lenses and other specialty designs, allowing for thinner profiles while maintaining the necessary optical performance. The choice of a 1.53 index reflects the industry’s pursuit of providing more lightweight and cosmetically appealing eyewear without sacrificing the quality of vision. Other indexes like 1.48, 1.50, and 1.55 exist but are either less commonly used or cater to specific niche applications in lens design, which do not represent the industry standard as effectively as 1.53 does.