Answer:

We offer these highest quality lenses: 

1.50 CR39 standard plastic 
1.61 mid-index plastic (20% thinner than 1.50 CR39)
1.67 high-index plastic (30% thinner than 1.61)
1.74 very high-index plastic (20% thinner than 1.67)

When you are ordering your lenses, our lens recommendation system will suggest the most suitable lens for your prescription.