Yes, you can get your lenses thinned down and to know more please refer to article what are Hi-Index lenses, and how do I know if I need them? 

If your prescription falls between SPH -4 to -6, we recommend 1.60 Index Lenses.

If the prescription is above -6 and below -10 then 1.67 Hi- Index lenses are recommended.

If the prescription is above -10 then 1.74 Hi-Index lenses are recommended.