"High index" means that the lenses are constructed of a plastic or glass material that has a higher index of refraction. The "index of refraction" refers to the speed that light travels as it passes through the lens material.

Myopia /and or astigmatism. In cases of myopia or myopia combined with astigmatism the edges of the lens are thick as the degree of myopia rises. The solution for more attractive lenses is to use lenses with a refractive index that is higer than the ordinary. The common lenses have a refractive index of 1,5. Today's technology can manufacture lenses with a reftactive index as high as 1,9. The suggested index to use depents on the degree of your myopia.

That means for degree of mypia:

• 0 - 2 , the suggested refractive index is 1,5 or 1,6,
• 2 - 3 the suggested refractive index is 1,6 or 1,7,
• 3 - 5 the suggested refractive index is 1,7
• 5 - 8 the suggested refractive index is 1,8
• > 8 the suggested refractive index is 1,9.

Hypermetropia and/or astigmatism.
In cases of hypermetropia over the 2-3 degrees of prescription we have the problem of the high central thickness. the result is , heavy lenses, magnification and distortion of your eyes. But there isalso another problem associated with not only the appearance of the glasses but with the vision as well. In such cases the ordinary sferic lenses present the so called sferical distortions at their edges. That means you will have distorted vision looking through these glasses looking at the left of right side.
The solution is to use high index lenses aspheric. The aspheric lenses have a different design that makes them flatter in order to achieve less thickness at the center. Yhe result is a thinner lens, lighter-weight, with less peripheric distortions and less magnification of the eyes. You can see clearly the difference in the vision performance on the two lenses in the pucture above.