Your Prescription
To place an order for prescription eyeglasses, you need to have a prescription for corrective eyeglass lenses and your pupillary distance. If you have a prescription for contact lenses, it cannot be used to make eyeglasses.
When you have your eyes examined, request your PD (Pupillary Distance) from the person performing your exam. Corrected lens eyeglasses cannot be made without it. It’s used to position the optical center of the lens when it is made so that you will be able to easily see through the eyeglasses. The correction in the eyeglass lenses is positioned in front of the pupil of your eye. Therefore, you cannot alter your PD simply to have it match the specifications of a frame that you might want (which will not accept your PD), because you will not be able to see through a lens produced from incorrect information.
The correct PD is particularly imporant for a multi-focal lens, as there are multiple viewing fields which are adjusted on the basis of the PD supplied.
The PD is frequently left off the prescription (although it’s usually recorded in your file), since having your PD empowers you to purchase eyeglasses from any supplier, not necessarily with the office of the person who does the exam.
PDs may be indicated in a variety of ways – You might be given numbers such as 63/60. This would mean that you use 63 as your PD for single vision distance, or a multi-focal pair of glasses. The smaller number would be used only when converting the prescription to single vision reading glasses. You may be given fractional PD measurements, right side and left side, and split PDs may be written as 30.5/31, for example.
Sph - Provides the depth of the focal field in the lens.
A negative sign in front of the number, indicates that you're nearsighted, which is the case with the majority of people who wear corrective lens. In nearsightedness, the thinnest part of the lens is the center, and the wider the lens becomes, the thicker it will be at the outer edge. If you're concerned about the outer edge thickness of the lens, you would be advised to consider narrower lens widths.
With a postiive sign preceding the Spherical number, you're farsighted, and the thickest part of the lens is in the center. The size of the lens is also important, because the larger the the lens, the thinner the edge will be. This may eliminate the consideration of half rim frames because the lens may become too thin to provide for the groove, to carry the filament, to help keep the lens in the frame.
Cyl and Axis - The two designations may be included if you have an astigmatism, an irregularity in the shape of the eye, which causes shape distortion in the viewed image. Cyl will describe the amount of correction you need to overcome this, and Axis is the angle at which the correction is placed. Note: If "DS" or "SPH" or "spherical" is noted in the Cyl space on your prescription, you have no astigmatism in that eye and the value to be entered is Zero.
The Axis will be recorded as a degree reading between 1 and 180 degrees. The Axis value is often times written as 3 digits on your prescription, which means if your Axis value is 5, it is often written as 005. Likewise, if your Axis value is 30, it will often be written as 030. Finally, an Axis value such as 120 will be written as 120.
Add - This is the reading portion of a lens in a multi-focal prescription, and this number indicates the strength of the overlay on the lens, for reading. It is typically the same positive number, for both eyes, although it may be written only once on your prescription. Add is often annotated "NV," as in "near vision." It may also be written as a large, positive number, across both the OD and OS lines of your prescription.
Extra Strength In ordering a pair of glasses, if your prescription strength is beyond the corrective capacity of a standard lens, an extra strengh charge will apply. This means the prescription entered contains values stronger than the standard limits for that lens. For production of these lenses, the glasses must go to our Custom Lab for special processing and can take approximately five days longer to deliver. There is an additional fee for these special lenses, the amount of which varies according to the type of lens and/or the strength of the prescription.
Please be advised that if your spherical corrections are very minor, making your "Add" the strongest corrective part of the prescription, you may find that the design of a lined Bifocal lens is more suitable to your needs rather than a Progressive (unlined) lens, as well as far more comfortable to wear. The reason is that your area of greatest need is minimized in the design of a Progressive lens (approximately the lower quarter and central third of the lens), while the lined bi-focal provides a larger, clearly delineated portion of the lens, for reading and other close work.
If you’ve had your eyes examined by a licensed Optometrist or Optician, they are required by law to provide you a complete written prescription. If you wear a multi-focal prescription, it’s in your best interest to ask for the basic, underlying multi-focal prescription (even if you simply want a single vision lens for a different purpose).
Multi-focal prescriptions may be modified for single vision use, or even a different multi-focal use, by working with the Sph and Add numbers. If there is a correction for astigmatism in one eye, or both eyes, those designations will not change, regardless of the depth of the focal field.
Single vision distance only – leave off the Add number and use the larger of the PD numbers if you’ve been given two.
Single vision computer glasses – Split the Add number in half, and combine that split number, with the Sph. Discard the remaining Add, and leave the Add data entry field blank. Use the distance PD, unless your monitor is virtually in front of your face, in which case, you may wish to narrow the PD a millimeter or two, for the sharpest focus.
Single vision reading glasses – Combine the Add and Sph numbers. In the case of the Positive Add and a negative Sph, net the difference, and the new number becomes the Sph. The Add data entry field will be blank, by virtue of it having been combined with the Sph number. If your Sph is already positive, you simply combine the positive Sph and the Add number, using it for the new Sph. The Add data entry field will be blank. For single vision reading only, you narrow the PD by 3mm from the distance vision PD.
Multi-focal Computer/Desktop glasses – To create this modification, you simply split the Add number in half (if there is no equal division of the Add number, you’ll need to decide if you want your focus closer or further, and the quarter diopter difference will shift the depth of the focal plane, accordingly) and combine half of the Add with the Sph. The balance of the Add will stay in that data entry field. Note: We do not create a multi-focal lens with an Add of less than +1.00. Use your distance PD, unless your monitor is extremely close (less than 18”), in which case, you may wish to narrow the PD by a millimeter or two.
Prism Corrections - We do not prepare prism corrections.
Glasses Without Correction in the Lens - It is quite possible to order eyeglasses with no prescription in the lens. You simply leave the prescription data entry fields defaulted to zero, but you will be required to enter a PD, to get the computer to process the order. Use 63, as it is a median number for an adult. It’s a good idea to include a note at the end of the order, in the Customer Comments section, indicating that this is an order for a pair of glasses with no correction in the lens. A pair of glasses ordered in this manner will have an optical lens, and may be worn.
If, however, you wish to order a frame only, for use as a replacement frame, for example, you may receive a -50% discount and the frame will be sent with a "filler lens," which may have writing on it, and will not be suitable for general wear. Again, please designate in the "Customer Comments" section of the order form, that you are ordering a replacement frame only, and wish the -50% refund.
NOTE: If you have questions about any of these modifications, you’re welcome to call the office (1.800.211.2105) during regular business hours (9-5 Pacific Time, M-F) and we will be happy to help with your questions. It is better to ask, than to order incorrectly. If you order incorrectly, it may be changed within a 24 hour period only, and you must notify us by e.mail. If you've ordered incorrectly, and it's beyond the 24 hour notification period, you may request a -50% refund, but there are no 100% refunds, or no-charge remakes, for errors in orders and/or prescription conversions.
Because of patient privacy policies, it is not the practice of Zenni Optical to contact your prescribing optometrist or optician. This is your personal responsibility. If you are unsure of what has been prescribed for you, please contact them directly to clarify either their penmanship, or the type of glasses they have prescribed for your use.
We suggest that when you receive your confirmation copy of your order, that you print it and put a copy in your medicine cabinet, so that you have your prescription, Pupillary Distance (PD) and all the details of your order for future reference. Zenni Optical is not responsible for your record keeping or for keeping your individual prescription information differentiated from that of other members of your family.
