A glasses prescription contains several key components that indicate the type and strength of lenses you need. Here’s how to understand it: OD (Oculus Dexter): Refers to the right eye. OS (Oculus Sinister): Refers to the left eye. OU (Oculus Uterque): Means both eyes (less commonly used in modern prescriptions). Common values include: SPH (Sphere): Indicates the level of nearsightedness (–) or farsightedness (+). CYL (Cylinder): Shows the amount of lens power needed to correct astigmatism. If blank, you likely don’t have astigmatism. AXIS: A number from 1 to 180 that specifies the orientation of the astigmatism correction. Only present if CYL is listed. ADD (Addition): Extra magnifying power for reading or close work (common in bifocals or progressive lenses), usually the same for both eyes. PD (Pupillary Distance): The distance (in millimeters) between the centers of your pupils. This ensures lenses are aligned with your line of sight. (Note: PD may not appear on all prescriptions but is often required when ordering glasses online.)