Prescription Limits and Lens Curvature
Prescription lenses are a fairly complicated business, and none are more complex than curved lenses for wraparound frames.
Lens Curvature and the Limits of Prescription Glasses
Most people think that prescription glasses are an exact science, and in some ways they aren’t wrong. The numbers written on your prescription are not a guideline; there are strict tolerances regarding how precise a prescription has to be.
On the other hand, two people with the same prescription may feel completely differently about the same pair of glasses. One might feel that the prescription is perfect, while the other is so uncomfortable that he or she can’t stand to wear the glasses for more than a few minutes. These are extremes, though the example is not an exaggeration.
When ordering prescription glasses in a wraparound frame, this disparity is acutely magnified. Prescription wraparound glasses (such as sunglasses frames, motorcycle glasses, and safety glasses) must be made with special and deliberate care to ensure that the patient can see and feel comfortable while wearing the glasses. Even then, there are a select few people who cannot get used to wearing prescription wraparound glasses, just as there are people who cannot adapt to progressive bifocals.
Here are good guidelines to follow when ordering prescription wraparound glasses online:
- Prescription power in this context is defined for each eye seperately. It is measured by adding the sphere and cylinder powers together. In example, -2.00 sphere and -2.25 cylinder in your right eye would equal a -4.25 power. On the same token, a +2.00 sphere with the same cylinder would add to only -0.25. Axis is not factored here.
- A lens’s “base curve” is defined as the amount of curvature of the front of the lens. Typically, the lens front is not altered during the prescription making process. All the power of the lens is worked into its back: the side facing your eyes.
- Higher base curves mean more curved lenses. A base curve of zero is as flat as glass on the front, whereas a base curve of 8 is the standard for many especially curved wraparound lenses in sports glasses.
- If you are ordering prescription glasses in a wraparound frame, you can expect that the prescription will have to be made into a curved lens of base 6 or 8. There are limits to the power of a prescription in this base curve. If your total prescription power in one or both of your eyes adds to anywhere outside the range of -4.00 to +3.00, you are at special risk of not adapting to wraparound lenses.
- Prescriptions with a power outside the range of -6.00 and +4.00 either cannot physically be done or are barely able to be done in a high base curve, depending on your prescription. The end result is, even if the prescription is made, it is highly unlikely that you will be able to adjust to the new lenses.
- People with prescriptions that have high cylinder (outside the range of -2.00 to +2.00) generally cannot adjust to a wraparound frame.
- Those who have prism are also at risk for being unadaptable to wraparound frames. Also, in general, prism causes the eyeglasses themselves to look strange or bad in a wraparound.
- If you have never had a wraparound prescription before and are on the border of one of these limits, it is good to be cautious. You may not be able to adjust to a wraparound prescription.
If you are curious about whether your prescription will work in a wraparound frame, it is a good idea to call us so we can have a conversation about it. We will be able to tell you whether or not wraparound style prescription glasses are right for you.
Occasionally, even people who have a very light prescription find that wraparound glasses do not work for them. This is not a matter of preference of lack of flexibility; it is simply an inexplicable issue that occurs for select individuals. There are no solid explanations, but it may have something to do with your ocular muscles or even something with the processing of your vision that occurs inside your brain. Whatever the reason, some people just aren’t right for wraparounds.
There are other options if you want a wraparound prescription in a curved frame and your prescription is too high. Give us a call or leave a comment if you’d like to talk about this. We hope this sheds some light on prescriptions in wraparound frames, and thanks for reading!