AR
= Anti Reflective and Anti Radiation coating
ONLY $4.95
Sunglass Tint = $4.95
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| Rx Terms |
Rx Terms and Abbreviations:
Add – Add refers to the near-vision correction in the prescription. The Add number changes the Spherical number, in that it is added to the Spherical number to create the near vision lens. It alters the focal depth of the field of vision.
Axis – Axis refers to the angle of the correction for the astigmatism in the eye.
BAL - This indicates that the eye for which the designation is made, is not sighted, and that the same numbers should be entered in both eyes, in order to have the lens match in appearance and weight. It would be advised to add a note in the "Customer Comments" section of the order form, after checkout, which eye is sighted and that the other is a "balance lens."
Bi-Focal - This refers to a lens with two separated fields of vision, one for distance, and the other for close work. The areas are specifically differentiated by a visible line. The area is approximately 14 x 28mm, and the top portion is approximately 40% up from the bottom of the lens. The actual height of the bi-focal area will be affected by the height of the lens chosen.
Cyl – Cylinder, referring to the strength of the correction for the astigmatism in the eye.
DS – In Latin, “Diopter Simplex,” meaning vision unaffected by an astigmatism. This abbreviation is usually placed in the Cyl column to signify no astigmatism in the eye. It may also be written across both the OD and OS lines, to indicate there is no astigmatism in either eye.
DV – Distance vision
Far Sighted - Your vision is most acute when looking in the distance. You may need correction to be able focus well, up close. Your prescription will have a postivie symbol in front of the Sph. The thickest part of your lens will be in the center.
Index - Generically speaking, index is an indication of the strength of prescription which may be accommodated by a lens without producing a thick and/or heavy result. A higher index lens is used for very strong prescriptions to minimize the visual appearance and physical weight, as well as to mitigate the distortion that some people experience at the edge of lens of great strength of correction, as our higher index lens are aspheric.
A higher index lens is not a "magic cure all" that will cause an extremely strong correction to become the slight lens of a minimum prescription strength. There are other factors involved in the resultant thickness of a strong prescription in a lens, most notably the finished size of the lens chosen, the size of the lens blank from which it's made, and whether the prescription is for nearsightedness or farsightedness.
If the prescription is strongly nearsighted, a secondary way of minimizing the thickness at the outer edge of the lens, is to choose a narrower lens (50mm rather than 52mm in lens width, for example, or 48mm rather than 50mm), since the thinnest part of a nearsighted lens is the center, becoming thicker at the outer edges as the width of the lens increases.
If the prescription is for a farsighted correction, the thinnest part of the lens is at the outer edge, thicker in the center of the lens. Similarly, however, the smaller the lens chosen, the smaller the blank that the lab may use to produce the finished lens. And the thinner the center will be. This is particularly important when considering a half rim frame; if the lens is very large, the edge may be too thin to successfully produce the groove to carry the filament which helps hold the lens in the frame.
For single vision corrections of great strength, Zenni Optical stocks both a 1.61 (+$17) and a 1.67 (+$37) higher index lens. Our standard lens is 1.57, used on all Zenni Optical glasses, a higher quality lens than the US standard of 1.49 index. The appropriate selection depends on the strength of the prescription. We use the 1.61 for prescriptions of +/- 3.50, and recommend the 1.67 once the strength has increased to +/- 6.00 in the spherical designation. It is not appropriate to automatically select a 1.67 index lens unless the prescription is of sufficient strength to warrant it. You do not get clearer, or better vision, with a higher index lens unless your prescription is of a strength appropriate to the index. The approximate reduction is 20% between 1.57 to 1.61, and another 20% from 1.61 to 1.67, but other factors also affect this, such as lens size.
At this time, Zenni Optical uses 1.57 lens for multi-focal corrections (lined bi-focals or progressive lens), although we will likely be adding higher index multi-focal lens in the future.
Multi-focal – This is a lens for correction of more than one field of vision. A lined bi-focal has both distance and close-up (reading) fields. A progressive has three fields of vision (includes a mid-range, which the lined bi-focal does not), and is characterized by the absence of a line.
Near Sighted - Your vision is most accurate, without correction, up close. You may need assistance in focusing properly in the distance. Your prescription will have a negative symbol in front of the Sph. The thinnest part of the lens is the center, and the wider the lens becomes, the thicker it will be. If lens thickness is of concern to you, and your prescription is strongly near-sighted, choose a narrow lens over a wider one, all other considerations being equal.
NV – Near vision
OD – In Latin, “Oculus Dexter,” meaning right eye.
OS – In Latin, “Oculus Sinister,” meaning left eye.
PAL – Progressive Adjusted Lens. Because of the limited reading area of a progressive lens design, the Add portion of a prescription is increased by a quarter of a diopter (typically) to compensate by increasing the size of the image. It does not change the size of that portion of the lens.
PD – Pupillary Distance (used to locate the optical center in the lens). Sometimes a prescription will list two numbers for the PD, such as 63/60. These two numbers refer to the distance vision PD (63) and then the near vision PD (60) which is generally a few millimeters smaller.
Photochromic - The generic name of the lens which darkens upon exposure to sunlight, to a sunlens, and clears when you are indoors. The lens darkens to approximately 65-75%.
PL – In Latin, “Plano,” meaning “flat.” In your prescription, it means there is no correction needed in that eye, and a zero should be entered in the data entry field.
Prism – A correction for split image vision. We do not prepare prism corrections.
Progressive - This refers to the design of the lens which includes three fields of vision, and the shape is approximately that of a funnel, the top portion being for distance, and the mid-range and reading areas narrowing, down the lens. The reading area is approximately the lower quarter, central third of the lens. It is a good design, without lines, for general use. People sometimes prefer a single vision lens for extended reading or up-close work.
Seg Height - In our multi-focal lens, the seg heights produced are standard. In a bi-focal lens, it's approximately 40% up from the bottom of the lens; in a progressive lens, the seg height is approximately 48% up from the bottom of the lens. The actual physical height, of course, will be determined by the height of the lens chosen. In most instances, if personal adjustment is desired, it may achieved by simply opening or closing the nosepads, changing the position of the frame on the bridge of the nose.
Sph – Sphere, referring to the refractive correction in the prescription. Also, sometimes “sph” is written in the Cyl portion of the prescription format, meaning that there is no astigmatism present in that eye. In that case, a zero would be entered in both the Cyl and Axis data entry fields, for that eye.
SV – A lens with correction for only one distance. May be for either reading, mid-range (computer) or distance vision, but only one.
Tri-focals - This refers to a lens with three viewing areas, demarcated by lines, for distance, mid-range and reading use. We do not prepare lined tri-focal lens.
“X” – On many prescriptions this symbol is written in front of the Axis number to designate “Axis.” The "X" is not necessary when entering the Axis value in the prescription box, only the number is needed.
“X” – May also be used to indicate “extra strength.” Actual meaning is determined by the location on the prescription. If the Spherical number is greater than +6 or -8, or if the Cylinder number is greater than +/-2, an "X" will appear on the order form, indicating that an extra strength lens must be used to accommodate your prescription requirement. If the glasses are to be made as a single vision prescription, this will incur an additional $9 charge.
If, however, your order is for a multi-focal (either a lined bi-focal or a progressive), high index or a photochromic lens, this extra strength charge is incorporated in the cost of the modified lens used.
V/A – Visual acuity, the degree to which vision is corrected by the lens containing the prescription.
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