Frame choice is very important, especially for high power prescriptions. People too often think lens thickness is all about material index and tend to overlook the importance of frame selection. In order to get the thinnest and most functional lens, we need to consider frame size, frame PD relative to patient PD, and frame shape. Large frame measurements, odd shapes, strong prescriptions and wide PD's can all contribute to lens thickness.
The fact is that the larger the frame the bigger the lens blank and the thicker the lens will be. One solution is to make sure the frame PD and patient PD are as close as possible. This means the pupils are centered in the frame lens. I recommend discussing this with your optician when selecting your frames. If your pupillary distance is wide (greater than 60), your lens may be thinner than if your pupillary distance is much narrower (54-60).
Generally speaking the higher the prescription, the thicker the lens is. The wider the pupillary distance, the lens will be thinner. Since the lens thickness increases as the frame size gets larger, it will utilize the side of the lens, which is also the thicker part. Therefore, for the same prescription and lens index, the larger the frame, the thicker the lens will turn to. Please also note that astigmatism can add extra thickness. Beyond -8.00, even a 1.74 index lens will be thick. Although we are trying to use large lenses for blocking light, we must also consider visual quality. Choosing a smaller frame and shape may be necessary if you have -5.00 or higher. Round or oval frames are best.