What are the thinnest eyeglass lenses available?

The thinnest eyeglass lens available as of 2015 is a high-index plastic lens with a 1.74 refraction index. The higher the index, the thinner the lens, and 1.74 is the highest refractive index available.

Eyeglasses correcting nearsightedness require lenses that are thin in the middle and thicker in the outer edges. The lens thickness increases with the severity of the condition, but high-index lenses refract light more effectively, allowing thinner edges and lighter lenses in higher prescription power corrections. High-index glass lenses are also thinner than conventional glass lenses, but glass is heavier than plastic, so there is not as much weight reduction as with plastic lenses.