Sphere (SPH): We cannot fill prescriptions with a SPH value stronger than -4.00 or +2.00. If you do not have astigmatism, the SPH will be the only value on your prescription (no CYL or Axis). Cylinder (CYL): If you have astigmatism in either eye, you will have a CYL value in your prescription. We cannot fill prescriptions with CYL value stronger than -2.00. While the above SPH and CYL values are at the extreme ends of our range, our ability to fill your prescription depends on your specific combinations of SPH and CYL values. If you SPH is stronger than -3.00 in either eye and you also have a CYL value, please give us a call at 800-525-4334, Mon-Fri, 8am-5pm PST. We are happy to help you figure out the best frames for you based on your prescription strength. We only offer single vision (distance prescription).