Common terms used on spectacle/eyewear/eyeglass prescriptions have the follow meaning:

• Pupillary Distance (PD): Pupillary Distance (PD) or inter-pupillary distance (IPD) is the distance (the industry standard is to measure in millimeters) between the centers of the pupils in each eye. A typical PD value is between 46 and 74. It is needed to ensure the center of each lens is aligned with the center of your pupils. Positioning lenses correctly in relation to the center of the pupils is especially important for higher-powered lenses due to the location of the optical center of the lenses. We would need your PD before we can place your order for prescription lenses. This is NOT part of your prescription and should be preferably obtained from your optician. If you do not have it now, please email that to us ASAP.
• Sphere (SPH): The sphere refers to the amount and type of prescription you require. Short-sight is corrected by negative (-) sphere values, long sight by positive (+). If the sphere value for one eye is negative, then the other is usually also negative and vice versa. If you only see one number for each eye on your prescription, it’s the “SPHERE” power. It is common for the doctor to leave out the decimal points. A number like -25 or +175 is the same as -0.25 or +1.75, respectively.
• Cylinder (CYL): The cylinder is only relevant if you have an astigmatism (or visual distortion). This value determines the strength of the astigmatism correction. If the cylinder value for one eye is negative, then the other is usually also negative, and vice versa. Prescriptions can be written in + cylinder construction (ophthalmologists write it this way) or – cylinder construction (the rest of the optical world writes in).
• Axis (AXI)– The axis value is the angle of the astigmatism correction. If you have a cylinder reading on your prescription, then you should have an axis reading. An axis of 5 (or 05) is the same as 005; 90 is the same as 090. 
• Reading Addition (ADD): The addition value is the amount of additional correction to add to the sphere value for reading or intermediate glasses. If you only see one ADD power, it’s understood that you have the same ADD for both eyes.

Pupillary Distance (PD): Your Pupillary distance (PD) is the distance, in millimeters, from one pupil to the other. A correct PD will ensure that the lens optical center (the point at which light enters the lens undistorted) is placed directly at your pupil. PD measurements are often taken individually for each eye.