Deconstructing Your Eye Glass Prescription.
When you purchase your new pair of eyeglasses and get a glimpse at the price tag, don’t get that “deer in the headlights” look of surprise and confusion. Did you know that your eye glass prescription is directly related to the cost of your eyeglasses? The reason being, the stronger your prescription, the more difficult they are to manufacture and the more expensive your set of eyewear will be. As an informed consumer, you should know your eye prescription, how to read it and how it relates to the price of your eyeglasses. By law your provider must give you a copy of your prescription if you ask for it, and knowing how to read it can help you understand a lot about your eyes.
Your visit with the optometrist or ophthalmologist consists of two exams. One is medically based, checking the entire structure of the eye for signs of disease such as glaucoma, cataracts, bleeding eye vessels (which would indicate diabetic retinopathy), or age-related macular degeneration (AMD). The other exam is a refraction test which will determine your eyeglass prescription. Answering the questions “which is better – this or that” as the provider flips through different lenses will result in your exact lens prescription.
If you need corrective lenses, then you were diagnosed as near-sighted (myopia), far-sighted (presbyopia) or as having astigmatism (when the cornea is shaped more like a football than a basketball). Here is what you need to know and how to read or translate an eye glass prescription.
- The term 20/20 vision refers to the eye chart (Snellen chart) in your doctors office which has a row of characters that a normal person should be able to see twenty feet away. 20/40 vision is only half as good as normal, and a person with 20/15 vision, has better than normal vision.
- The doctor will determine a “sight distance” for you and it is shown for each eye. The abbreviations listed usually to the left, in two rows, “O.D.” and “O.S.” each stand for right eye and left eye respectively.
- The first column labelled “SPH” which stands for “sphere”, indicates the refractive power. This is basically the amount of lens power needed to correct your vision problem. If this number (measured in units of “dioptics”), has a minus sign (-) you are near-sighted. If it has a positive (+) or no sign before it, that means you are far-sighted.
- The higher the dioptic number, either positive or negative, the greater the lens power needed to make correction. If you’ve have a -2.00 D, then you are considered mildly nearsighted and the less your lenses would cost. If you have a +8.00 D, then you have a far greater degree of farsightedness.
- The next two columns on your prescription would apply if you have astigmatism. They are abbreviated “CYL” and “AX”. Your cylinder correction number will determine how well or poorly your eye focuses light onto the retina. Written with either a (+) or (-) sign, and the larger the number the greater the astigmatism. The axis will be a number between 0 and 180 which shows the degree of orientation on which the miscurvature of the eye takes place.
- Therefore, an astigmatism reading of -2.50 D x +5.00 D x 60 means the person has 2.50 dioptics of nearsightedness with +5.00 dioptics of astigmatism along a 60 degree axis.
- For bifocal or progressive lenses, your provider will have an additional value in a row labelled “ADD”. This number is the amount of additional correction your eyes need to focus at close distance. You now have one prescription for regular vision and one prescription for reading vision.
- The abbreviation “PD” or pupilary distance, is the the distance between your pupils and is measured in millimeters. When making your set of eyeglasses, this number will be used by the technician to correctly set the focusing power of your prescription at the center of your line of sight.
Not only does the power of your lens effect the price, eye glass lenses get progressively more expensive from single vision, to bifocal, to progressive. Contact us to learn about the options available to fit your eyeglass prescription.