You just had your eye exam, which is fantastic because your eyes are very important, and now you are handed a nifty paper with your prescription. You understand that if you go to an optical store with your prescription you can pick the pair of glasses you love or the contacts you may prefer. All this is great but they are your eyes and being knowledgeable about them is your right so what does your prescription really mean?
OD and OS and the occasional OU
One thing you may notice immediately is the letters OD and OS, hmmm….yes of course everyone knows what this stands for! Really this is unknown to (almost) everyone until they get their first prescription and ask what the heck it means. These are optometric abbreviations. OD stands for oculus dexter referring to the right eye. OS stands for oculus sinister referring to the left eye. Some prescriptions may have the abbreviation OU, which stands for oculus uterque which means “both eyes.”
If this is not your first prescription then you may have noticed that the OD information comes before the OS information. The reasoning behind this is to avoid making errors. Eye doctors write prescriptions how they view your eyes. People read left to right so when an eye doctor looks at your eyes, facing you, they look at your eyes from left to right, meaning they see your right eye on their left and then your left eye on their right.
DV and NV
DV stands for Distance Vision and NV stands for Near Vision. DV is where your prescription goes. NV is used if you have glasses only for reading or if you have bifocals; it indicates the lower portion of your bifocal lens.
Every optical prescription is based upon spherical and cylindrical power using diopters (D) as the form of measurement. SPH is the abbreviation for sphere. This indicates the amount of lens power to correct the refractive error of the eye; nearsightedness (-) or farsightedness (+).
Nearsightedness or myopia is when one is unable to see distant objects clearly. Farsightedness or hyperopia is when one is able to see things that are far away more clearly than things that are near.
PL stands for Plano which indicates that you are neither long nor short sighted but zero power for the Sphere, however you may have astigmatism.
The term sphere means that the correction for the farsightedness or nearsightedness is equal in all meridians of your eye. Meridian means “direction”like on a protractor. Meridians of the eye are determined by superimposing a protractor scale on the eye’s front surface. The 90-degree meridian is the vertical meridian of the eye, and the 180-degree meridian is the horizontal meridian. Sphere means the Rx is equal in all directions (for all angles).
The abbreviation CYL refers to the cylinder. The cylinder power always follows the sphere power in your prescription. The cylinder corrects astigmatism or refractive error along a specific axis from 001 to 180 degrees. If this section of your prescription is empty you either do not have astigmatism or it is so minor it was not necessary to correct it. If the number within the Cylinder column has a minus sign (-) this is to correct nearsighted astigmatism. If the number has a plus sign (+) it is to correct farsighted astigmatism.
Some eyes have two different curves on a single refracting surface on or within the eye, this is known as astigmatism. Consider if the front surface of the eye or cornea does not have a surface like a spherical ball, such as a baseball, instead is shaped like a football; then there would be two different curves to consider. One curve is from the tip to the other tip of the football and the other running around the central part. Each of these has its own radius of curvature. If any refracting surface of the eye is other than spherical then light will not be able to form a single point of focus on the retina; hence astigmatism.
The axis is the angle for the correction of the cylinder (astigmatism) specified from 001 to 180 degrees. It is the orientation of the astigmatism. The number has no relevance to the size of the astigmatism.
The Add is the addition to the distance prescription. It is the added magnifying power applied to the bottom part of the lens, specifically a multifocal lens to correct presbyopia.
Presbyopia is a vision condition in which the crystalline lens of your eye loses its flexibility. This makes it difficult to focus on close objects. Do not be alarmed presbyopia is a natural part of the aging process of the eye.
The number in this section is always a plus (+) power, even if it is not indicated with a plus sign. If any number in your prescription under Sphere, cylinder or add does not have a minus sign (-) nor a plus sign (+) than it is always a plus sign.
This is not often used except when necessary. It is designed to treat errors in orientation of the eyes or strabismus.
Strabismus is a condition in which both eyes do not look at the same place at the same time. An eye may turn in, out, up or down. It is usually caused by poor muscle control or a high amount of farsightedness.
Prism is the amount of prismatic power, measured in prism diopters, to compensate for eye orientation problems. The base indicates the direction on which the prism takes effect. There are four abbreviations used for prism direction. BU stands for base up, BD stands for base down, BI means base in and BO is base out.
Eyeglasses vs. Contacts
An eyeglass prescription is for the purchase of eyeglasses only. It does not contain pertinent information for a contact lens prescription.
A contact lens prescription specifies the base curve (central) of the back surface of the contact lens and the lens diameter. In addition, the contact lens prescription will specify the manufacturer and brand name of the lens.
An eyeglass lens prescription is modified when determining the contact lens power; an eyeglass lens is worn at a distance from your eyes whereas contacts lenses are worn on the cornea of the eye.
A contact lens prescription can only be written after your doctor or optician does a contact lens fitting. Your eyes need to be evaluated for the response to the lenses as well.
Now you have an idea of what your prescription means. A little knowledge can go a long way. Remember your eye doctor is there to help, so if you have any questions please do not hesitate to ask them. Caring for your eyes is a team effort! Stay informed and develop a good relationship with your eye doctor.