The distance between the back surface of the lenses and the front of the eyes is called vertex distance. Metal frames have nose pads which cause a greater distance. While plastic frames have a shorter distance so people with high myopia will find plastic frames more suitable. What's more, some metal frames have unadjusted nose pads, which can not fit their noses properly so they always get poor vision with metal frames. However, Plastic frames can always stay at a right place without adjustment of the nose pads.
Some high myopes find that they can see better with plastic frames rather than metal ones with nose pads. The distance between the back surface of the lenses and the front of the eyes is named vertex distance, which can be increased by equipping nose pads in metal frames. Plastic frames with a shorter vertex distance are more suitable for highly myopic people. More specifically, some metal frames have unadjusted nose pads, creating a greater vertex distance and making the wearer see a poor-fitting bridge easily. Plastic frames do not involve any nose-pad adjustment and the bridge will always stay at a right place.