My prescription says my SPH is -8.00, and my optician told me I should choose 1.61 lenses for my new eyeglasses, because this kind of lenses are much thinner than ordinary lenses such as 1.499 or 1.56, any one can tell me more about this kind of high-index lenses?

High index lenses are thinner than common lenses,especially if the prescription value is over -500,the difference will be more obvious.

I.61 or 1.67 are the "index of refraction" of the eyeglasses lens material, the index is a ratio that compares the speed of light when it travels through air and the clear material, the higher this index is, the thinner and lighter the lens will be, so if you have a SPH more than -7.00, I will suggest you to choose high index lenses.