An eye prescription holds the readings that your optometrist records each time you go for an eye test. These numbers on the prescription slip/card are the key to your correct power. Whenever you wish to buy power eyeglasses/sunglasses, these values come in handy. It might look tricky at first, but there’s an easy way to decode these abbreviated terms & set of +/- readings.
SPH or Sphere is the power of the lens required to correct a single vision defect. This denotes if a person has myopia or hyperopia. It is measured in Diopters (D). The values can be different for both the eyes.
CYL or Cylinder power indicates that the cornea of the eye is not perfectly sphere in shape. If you have some numbers in your CYL grid of your prescription, you will require eyeglasses to correct astigmatism.
Axis reflects the exact orientation of your astigmatism. It is measured in Degrees. If your prescription has a CYL value, it is sure to have an axis value too. If your prescription holds a CYL value and no axis or vice versa, it means your prescription is either incomplete or incorrect
Add or Near Addition power is added on the lower part of the multifocal/bifocal lenses to correct presbyopia. This helps one in performing close-up tasks with ease.
Pupillary distance is an important measurement from the center of one eye to the center of another. This is used to mark the exact optical center in your lenses which further helps to view things properly and without any eye strain.
A prescription for Power Eyeglasses/Sunglasses is different from that of Contact Lenses. Since contact lenses are placed on the eyes, in direct contact, the values are changed accordingly by your optometrist to give you utmost vision clarity and wearing comfort. So, it is advised to not use the same prescription for both contact lenses and powered eyewear. Do let your optometrist know that you’re switching to either one of them so that he can correctly record your eye power.