If you’ve got a stronger prescription, you’ve probably been offered “high-index” lenses at some point. It’s a term that gets used constantly and explained rarely, so here’s what it actually means.
What the index number refers to
The refractive index of a lens material describes how efficiently it bends light. A higher index means the material bends light more per millimetre of thickness, which means a thinner, lighter lens can achieve the same optical correction as a thicker one in standard material.
Why this matters for stronger prescriptions
The stronger your prescription, the more curvature a lens needs to correct it, and the thicker a standard lens becomes at its edges. High-index materials let that same correction happen in a slimmer, flatter lens — which sits more comfortably in the frame and looks noticeably less bulky.
Is it worth it for milder prescriptions?
For lower prescriptions, the difference is often minor enough that it’s a matter of preference rather than necessity. For stronger prescriptions, it usually makes a genuinely noticeable difference to both comfort and appearance.
The trade-off worth knowing
High-index lenses are generally lighter and slimmer, but they can be a little less impact-resistant than some alternatives, and they do typically cost more. It’s worth weighing lifestyle and prescription strength together rather than assuming higher is always better.
We’ll always talk you through what’s actually necessary for your prescription specifically, rather than defaulting to the most expensive option.