If you've been shopping around for a new pair of shades, you may have come across frame descriptions that include a base curve measurement. What is it? Why is the base curve important? And how does it impact your decision? In this blog, we'll cover all the nitty gritty details.
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In the video below, Eyeglass Tyler dives into the different styles of base curves and why you may prefer one over the other. If reading is more your style, continue on to find out all the details.
Our peripheral vision plays a big part in what we see. Try looking through narrow lenses, or using your hands to block the sides of your face. It's uncomfortable because you innately know there's so much more to see than what's straight ahead. This is why lens designers have created frames with a range of base curves. The base curve is the measurement of the lens curvature or how much the lens curves to the shape of the face. Depending on how high or low the base curve is indicates how curved or flat the frame and lenses will be.
There are 4 main base curves—4, 6, 8, 10—each with its own pros and cons. Knowing which to look for is vital because it impacts the finished optics, fit, and cosmetics of your new prescription glasses.
A 4-base curve is the lowest and flattest base curve we'll cover today. It is typically found in ophthalmic frames or eyeglass frames. The flatter a frame is, the higher a prescription it can take which makes the 4-base a great choice for everyday eyewear. As you can imagine, the flatter a pair of glasses is the further it sits from your eyes, especially along your peripheral vision. This can leave the sides of your eyes open to unwanted light or debris. For eyeglass, light coming in from the sides isn't typically a problem, as the lenses are clear and you mostly use them indoors.
Below are examples of 4-base frames from a side view, to easily see the curvature of the frames and lenses.
Oakley Wheel House
Wiley X Contour
A 6-base curve is a medium base with a minimal curve. If you have a high prescription, the flatter base curve will accommodate the stronger correction. However, the lower the base curve, the more light will be let in through the sides of your sunglasses. Fashion and lifestyle sunglasses most often utilize a 6-base curve because their style is just as important, if not more, as their function.
Below is an example of a 6-base frame from a side view to easily see the curvature of the frames and lenses.
An 8-base curve is considered high and creates a wraparound frame shape. An 8-base curve provides the most protection from the sun and allows the frames to hug your head, which is why most sport glasses utilize an 8-base, or even a 9-base frame. While not as typically as prescription friendly as its 6 and 4 base counterparts, 8-base frames can handle a wide range of prescriptions.
Below are some examples of 8-base frames from a side view to easily see the curvature of the frames and lenses.
Costa Half Moon
The highest wrapped frames on the market are 10-base, typically only found in shield style sunglasses. While these may be some of the coolest style wise on the market, they are usually not available in prescription. There are a few ways around this roadblock, such as Rx inserts, but it varies based on brand and frame style.
Below is a 10-base frame, with a side view to see the extent of the side coverage.
Oakley M2 ANSI
If you are looking for eyeglasses, a 4-base is the way to go. All of the features that make up a great pair of eyeglasses come in the 4-base frames.
For everyday sun protection, a 6-base frame is the standard sunglass lens curvature. It gives you a natural view of the world and protects your eyes from UV rays and harsh light. A lower curve is generally easier to get acclimated to in a new pair of glasses. The downside is, at times you're exposed to more light than you would like.
If you're participating in an outdoor sport like fishing, you'll need to choose an 8-base frame. They provide the coverage you need to keep out unwanted sunlight and even debris that threatens to get in your eyes. Sport sunglasses need to be able to stay in place while you're in motion, and the 8-base curve wraps them around your head for a snug yet comfortable fit, you'll forget they're there.
The higher the base curve, the more challenging it is to perfect your prescription without distortion. This wrap distortion is combated with digital surfacing lens technology; it takes into consideration the frame's curve and prescription strength and adjusts the prescription to counteract that curve. more optically clear lens along the edges. Check out the Digital Lenses for High Wrap Frames blog to learn more details on how digital lenses work, and why you may want to get them.
Finally, 10-base frames look cool, give great coverage and protection, but don't come in prescription. If you do need prescription sunglasses, there are many great frames and styles to choose from, just not many within the shield sunglass world.
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