How To Read Your Prescription
A prescription for soft contacts includes a particular brand, as not all styles and materials are the same, and a number of other measurements per eye such as the curvature and diameter of the lens.
The prescription also includes:
Right Eye (OD)
OD stands for oculus Dexter, the Latin phrase for “right eye.” This abbreviation precedes the prescription information for the right eye, which is always listed first.
Left Eye (OS)
OS stands for oculus sinister, the Latin phrase for “left eye.” This abbreviation precedes the prescription information for the left eye, which is always listed second.
Both Eyes (OU)
If both the left and right eye has the same diagnosis and prescription information, the abbreviation “OU” is used instead, or “ocular uniter,” meaning both eyes.
The spherical power, indicated on the prescription as power “PWR” or sphere “SPH”, of a soft contact lens is calculated in a unit of measurement equal to the reciprocal of the focal length of a lens called a diopter “D”. The spherical power of a lens is indicated with a plus sign (+) for hyperopia and a minus sign (-) for myopia.
Commonly known as near-sightedness or short-sightedness is a condition of the eye where the light that comes in does not directly focus on the retina but in front of it, causing the image that one sees when looking at a distant object to be out of focus, but in focus when looking at a close object. The opposite of myopia is hyperopia (long-sightedness).
Hyperopia or Hypermetropia
Commonly known as being farsighted or longsighted, is a defect of vision caused by an imperfection in the eye (often when the eyeball is too short or the lens cannot become round enough), causing difficulty focusing on near objects, and in extreme cases causing a sufferer to be unable to focus on objects at any distance. As an object moves toward the eye, the eye must increase its optical power to keep the image in focus on the retina. If the power of the cornea and lens is insufficient, as in hyperopia, the image will appear blurred. The opposite of hyperopia is myopia.
Defined as an optical defect in which vision is blurred due to the inability of the optics of the eye to focus an object into a sharp focused image on the retina. This may be due to an irregular or toric curvature of the cornea or lens. The two types of astigmatism are regular and irregular. Astigmatism can be corrected by toric contact lenses.
Abbreviated “BC,” the base curve of a lens indicates the curvature on the inside of a lens. This measurement is noted in millimetres, usually between 8 and 10, and attempts to come as close to the curve of the eye as possible to ensure the greatest fit and comfort. If the cornea is more bulged or curved, this number will be lower. BC median refers to a base curve 8.7 mm.
Abbreviated “DIA” the diameter of a lens measures the width of a lens in millimetres, from end to end. The average size of a contact lens is between 13.5 and 15 millimetres.
For individuals with astigmatism, the cylinder power of a lens measures the degree to which a lens must account for astigmatism. The cylinder is an oval band on a lens that enables an individual to see all ranges clearly at once and is measured in diopters, like spherical power. The cylinder power of a lens is typically expressed with a minus (-) sign and is always written separately from the sphere power to avoid confusion.
The axis (AX) indicates the orientation of the astigmatism, a measurement that designates where the cylinder correction should be located. Generally, the cylinder runs up and down or side to side, at 90 degrees or 180 degrees.