An eye prescription precisely measures the optical power needed for clear vision. It translates comprehensive eye exam findings into a standardized format that opticians use to craft eyeglasses or contact lenses. This document ensures light entering the eye is properly focused onto the retina, correcting refractive errors that cause blurred vision.
Key Abbreviations and Their Meanings
Understanding eye prescription abbreviations is key to deciphering its details. “OD” (Oculus Dexter) refers to the right eye, and “OS” (Oculus Sinister) indicates the left eye. “OU” (Oculus Uterque) applies to both eyes, though separate entries for OD and OS are common.
“SPH” (Sphere) indicates the main lens power for nearsightedness or farsightedness. “CYL” (Cylinder) represents lens power for astigmatism. “AXIS” specifies the orientation of astigmatism correction in degrees. “ADD” (Addition) refers to extra magnifying power for near vision. “PRISM” indicates correction for eye alignment issues, and “PD” (Pupillary Distance) signifies the measurement between pupil centers.
Interpreting the Core Numbers
The numerical values associated with these abbreviations provide the precise details of your vision correction. The “SPH” value, measured in diopters, indicates the strength of the spherical lens for correcting nearsightedness (myopia) or farsightedness (hyperopia). A negative sign (-) signifies nearsightedness, meaning distant objects appear blurry. A positive sign (+) or no sign indicates farsightedness, where close objects may be unclear. Higher values reflect a stronger correction.
The “CYL” and “AXIS” values correct astigmatism, a condition where the eye’s cornea or lens has an irregular, football-like shape. The “CYL” number, in diopters, specifies the lens power to compensate for this uneven curvature. If this column is blank, astigmatism correction is not required. The “AXIS” value, measured in degrees from 1 to 180, defines the exact orientation at which the cylindrical correction should be placed on the lens. This precise angle ensures the corrective power aligns accurately with the astigmatism in your eye, sharpening vision.
“ADD” (Addition) is a value in prescriptions for multifocal lenses, such as bifocals or progressive lenses. This positive number, typically ranging from +0.75 to +3.00, represents additional magnifying power for clear near vision. It addresses presbyopia, the age-related hardening of the eye’s natural lens that makes focusing on close objects difficult. This value is usually the same for both eyes.
“PRISM” corrects eye alignment problems like strabismus (crossed eyes) or double vision (diplopia). A prism lens works by bending light before it enters the eye, redirecting it to ensure that images from both eyes align correctly on the retina. This helps the brain fuse the two images into a single, clear picture, reducing eye strain and eliminating double vision. The prism value is expressed in prism diopters and includes a “base” direction (e.g., Base In, Base Out, Base Up, Base Down) indicating where the thickest edge of the prism should be positioned.
Understanding Pupillary Distance and Beyond
“PD” (Pupillary Distance) measures the precise distance between the centers of your pupils, typically in millimeters. This measurement is important for the accurate placement of the optical centers of your lenses, ensuring they align directly with your pupils for optimal clarity and comfort. An incorrect PD can lead to eye strain, headaches, or blurred vision, even with an otherwise accurate prescription. While sometimes included on the prescription, it may also be measured separately by an optician.
An eye prescription is a technical document focused solely on correcting refractive errors and is not a medical diagnosis of any underlying eye disease. Regular comprehensive eye examinations are important to update your prescription as vision changes and for eye care professionals to monitor overall eye health, detecting potential conditions early. Prescriptions typically have an expiration date, often one year, highlighting the need for periodic check-ups to maintain vision and eye health.