Yes, high index lenses are thinner than common lenses which are suitable for those short sighted people with high prescription. Usually the common eyeglasses will be made with thick lenses for the high prescription. That is why they need to use the high index to make their eyeglasses look thin and light which will make them wear comfortable and convenient. Usually if the prescription is above 1000, the eyeglasses with 1.74 high index lenses will be suitable. Whatever the material or the design, the high index lenses are the first and important choice for those people with high prescription. It is really good at the quality.
Well, of course not all the people are recommended to have high index lenses. Generally speaking, high-index lenses are an alternative choice to standard, plastic eyeglass lenses. And for the benefit of wearing them I have to say that they are specially designed for individuals with a strong prescription. In detail, you should know that high-index lenses are able to bend light to a stronger degree than a lens with a lower index, therefore the higher the index of the lens the less material needed to achieve a given prescription. So people which strong prescription can just have a try. Also, they can reduce the thickness and weight of an eyeglass lens, and that can be amazing.