Lens index is a number that describes how thick or thin your lenses are. The higher a lens index is, the thinner it becomes.
/media/catalog/product/cache/e228
How to choose the best lenses for your glasses
How to Choose the Best Eyeglass Lenses
John Lewis Opticians
Prescription lens thickness, What you need to know
Complete Pricing Guide, Buyer's Guide
Lens packages explained
What affect the thickness of glasses lenses?
High-Index Lenses - All About Vision
What Camera Lens Should I Buy? A Beginner's Guide
Ordering Warby Parker glasses online with a challenging
Difference between spherical and aspheric lenses