Which lens index is commonly chosen to reduce thickness for strong prescriptions?

• A. 1.60
• B. 1.74
• C. 1.50
• D. 1.67

Answer: (D)

Higher index lens materials bend light more efficiently in a given thickness, so for the same strong prescription you can achieve the needed power with less material. This makes the lens thinner and lighter overall. Among common indices, 1.67 is a popular choice because it provides a good balance between thinning the lens and keeping cost, durability, and optical quality reasonable. While 1.74 would yield even thinner lenses, it tends to be more expensive and can be more prone to brittleness and edge-thickness issues in certain prescriptions; 1.60 is thinner than standard 1.50 but not as effective at thinning strong lenses as 1.67; 1.50 is a lower index and results in thicker lenses for strong corrections. Thus, 1.67 is commonly selected to reduce thickness for strong prescriptions.