As its name implies, Overnight Glasses can make you a new set of prescription glasses quickly -- and really quickly if you're willing to pay extra for a new pair of glasses. If you buy a frame/lens package, fast three- to four-day service is available for $9. (It takes slightly longer for progressive lens and bifocal lens types.) The quality of the lenses I got was as good as that from other replacement lens sites, so there's no sacrifice of prescription eyewear quality for speed.

As for new lenses for your current frame, you ship your frames to Overnight Glasses and it'll replace your lenses with new ones in 48 hours. The service can do polarized, blue light, transitions and many other types, though progressives take an additional two days (so 72 hours total from the time your frames are received).

If you're looking for a truly overnight option, the emergency, 24-hour rush service costs an additional $60 for single vision. As noted, a progressive lens order can take an additional two days, so the fastest you can get new progressive lenses is three days.

Overnight makes lenses for Bose Frames and Amazon Echo Frames audio glasses.

Notable site features: The site has a clean look and is easy to navigate. There are multiple shipping options. 

Eyeglasses.com has a huge selection of both frames and lenses and is also one of a small number of sites that offer a lens replacement service for existing frames, with prices starting at $48. As with all the other sites here, you simply choose the lens you want (that can be a little daunting because there are so many options) and you'll get sent a prelabeled box with which to return your frames, with free shipping both ways. If you don't know your prescription -- and don't want to change your current prescription -- you can opt to have Eyeglasses.com's technicians "read your lenses and duplicate them." 

The service isn't superspeedy in terms of turnaround time, but the lenses are high-quality and the eyewear site has good online help options, including a Replacement Lenses Wizard and an online chat feature. Unlike Lensabl, which highlights its lens replacement service, Eyeglasses.com doesn't market the option front and center. 

Eyeglasses.com makes lenses for Bose Frames and Amazon Echo Frames audio glasses.

Notable site features: Eyeglasses.com says it only sells "high-quality, individually made lenses made in the USA," and the sample glasses I tried had excellent lenses that gave me a very sharp image. There's a huge selection of lens options, and you get a "Perfect Lenses Guarantee" that allows you to send your glasses back if they don't work for you -- you can get a redo or a full refund, your choice.

Current deals and coupons: 15% off for new customers in exchange for your email address.

While it's had shops in the New York area for a while, ReplaceRxLenses is somewhat new to the online replacement-lens arena. My experience using this retailer was smooth, with a relatively quick turnaround time (about a week, but I was in New York). Its prices are competitive and slightly cheaper for some lens types.

The site says what differentiates it from competitors is that it doesn't have an assembly-line format for fulfilling orders, where one worker is responsible for manufacturing the lenses, another is responsible for tracing the frame and edging the lenses to fit the frame and another might handle the final eyeglass inspection. "With us, one technician works on a customer's order from start to finish," a rep told me. "We believe this format results in a better end product, because there is almost no chance of information being lost or mistakes being made along the way."

ReplaceRxLenses says it can do a replacement for prescription eyewear or replace nonprescription lenses for Bose, Amazon Echo, Snapchat Spectacles and many other audio/smart frames.

Notable site features: The site says it has experience working with frame types and lenses that some other places can't handle. "We have plenty of experience working with sports frames, wraparound frames, vintage frames and extended range prescriptions," a rep told me. "Many other online replacement services can only work with certain frame types and up to certain prescriptions."

The site tries to get as much information about a customer's frame beforehand so it can begin working on the order even before receiving the frame, which helps expedite the order. (I submitted a photo of my frame.)

Current deals and coupons: 15% off for new customers or 10% off for returning customers in exchange for your email address (leave site to see offer).

LensDirect says it can make quality lenses for a wide array of frames -- "practically any frame unless it just absolutely doesn't make any fundamental sense like putting a +7.5 prescription on a semi rimless frame" -- and has its own machine in-house that can cut the lenses anytime (other retailers have this as well). "We make lens replacement more affordable than our competitors without sacrificing quality," a rep told me.

LensDirect does now make replacement lenses for Bose and Amazon audio glasses, though it does require you to sign a waiver to work on them.

My lens replacement took about a week, and the lens quality was high. After using discount codes, the cost for lenses I got was a bit less than from some competing sites like Lensabl.

Notable site features: The site has a virtual try-on feature if you're buying a frame and lens package. When it comes to an older audience (people who wear progressive or bifocal lenses), lens options tend to be more affordable (with discount codes applied), specifically when it comes to the 1.67 high-index lens, which is 40% thinner and lighter than a standard CR39 lens. "Even to a younger audience who wants to take a cheap eyeglass frame and get exactly the lens they need, our CR39 and Polycarbonate lenses start off more affordable even for them," a rep said.