Lens Thickness and Refractive Index

The index of refraction (also called the Refractive index) is a measure of how efficiently a lens material can bend light. The index of refraction of eyeglass lens materials usually ranges from 1.50 (regular plastic) to 1.74 (one variety of high index plastic)

The following table shows some of the more popular high index lenses currently sold Thickness values are based on the overall front-to-back thickness of Single vision lenses in an average-size frame

Lens Material	Refractive Index	%Thinner than Plastic Lenses
1.74 high index plastic	1.74	up to 65%
1.71 high index plastic	1.71	up to 60%
1.67 high index plastic	1.67	up to 55%
1.60 high index plastic	1.60	up to 45%
Polycarbonate	1.59	up to 40%
1.54-1.56 high index plastic	1.54 - 1.56	up to 30%
glass	1.52	---
plastic	1.50	--

 

Most aspheric lenses also are high-index lenses. The combination of an aspheric design with high-index lens materials creates a lens that is noticeably slimmer, thinner and lighter than conventional plastic lenses.