18B. If we instead put the special surfaces on the outside, and have a sphere or cylinder in the middle, the there is no gap as indicated in FIG. 18C. If the bottom lens is flexible, however, then we can bend the back lens so that there is no significant gap even with the ...
Cylinder (CYL) Cylinder indicates the amount of lens power needed forastigmatism. It always follows the sphere power on an eyeglass prescription. The number in the cylinder column may have a minus sign (for correction of nearsighted astigmatism) or a plus sign (for farsighted astigmatism). If ...
Cylinder (CYL) Cylinder indicates the amount of lens power needed forastigmatism. It always follows the sphere power on an eyeglass prescription. The number in the cylinder column may have a minus sign (for correction of nearsighted astigmatism) or a plus sign (for farsighted astigmatism). If ...