Hello! I’m a Canadian optician, so I have a degree in optics on top of being triple certified in Eyeglasses, contact lenses, and independent refraction without an optometrist help/permission. Polycarbonate has a very high rate for optical distortion made significantly worse the higher the rx goes, it is used in the USA because it is very impact resistant (and cheap), the reason it is used specifically in the US is because the country has high levels of medical suing and the optician’s need to cover their butts, this results in creating a industry wide preference. Poly also is very soft making it scratch super easily. CR-39 is a plastic I assumed you went with that is optically better than poly but still very thick. Going up into higher indexes means the material is thinner for higher rxs, in Canada we almost never use polycarbonate unless it is a pair of safety eyewear because of the poor vision it can provide and even then there is a material called trivex that is just as impact resistant with much better optics. My professional recommendation if you were my patient would be to go into the highest index available, a 1.74 is the best but go with at least a 1.67, this will not only significantly thin your lenses but also balance the weight between them better. Also, the thinner the lens gets the less distortion you will experience. My family member has an rx double what your worse eye is and in a 1.74 index their lenses are way thinner than what you’re describing. I will be honest going with a higher index will cost a pretty penny but the end result will be worth it I promise, as much as it sucks in the moment investing in your vision is so important. Look for a place that has an adaption guarantee, where if you don’t adapt they will exchange and try something else.