The difference between 1.67, which is considered regular index and 1.74 is quite small, and really, the only way you'll notice the difference is if you have a prescription below a -6 or above a +4. However, if you are in need of a very strong prescription, it is absolutely worth the additional cost! High Index 1.74 lenses are the thinnest, flattest, and most cosmetically appealing lens ever developed. Higher myopes will experience a minification from their lenses. As the lenses get stronger in lens power the eyes look smaller. ... This effect is the result of a shift in the periphery of the lenses. The bigger the lens the stronger this effect will be in the periphery.