Lens index describes the thickness of your optical lens - a higher lens index indicates a thinner lens. Lenses with a high index are thinner and more powerful. They're light and fashionable, but they're mostly recommended to those who require a higher vision correction. While multiple indexes can be used for most prescriptions, it is up to you to decide which one fits your personal needs.
The difference in lens index can have a huge impact on how your glasses look. Your prescription and lifestyle determine the kind of lens index that you might need for your glasses. While thicker lenses are economical, they are only suitable for people with lower vision correction needs. Higher index (thinner) lenses are lighter and more fashionable and can meet a wide range of vision correction needs, including high prescriptions.