Buying eyeglasses online sounds like a convenient, less expensive and fun way to get new ­eyeglasses. True, but avoid the pitfalls …

Prescription: Basic prescriptions for nearsightedness or reading are easier to fill online. A complicated Rx, such as for astigmatism or progressive lenses, is more risky. 

A key measurement is pupillary distance—the millimeters between the centers of your pupils. Online stores let you capture this with a ruler and your phone or computer camera. Better: It is most accurate to have your eye doctor provide it with your prescription. 

Frames: Sites let you upload your photo to try frames virtually. To know how they feel, Warby Parker and Felix + Iris lend you frames to try at home. 

More cautions…

You could purchase frames online and have a local optician do the lenses, but they may not work on frames that they didn’t sell you. Expect to pay for their time and expertise, and the risk is yours if the frames break while being worked on.

Compare policies. Warby Parker, Ambr Eyewear and Felix + Iris offer 30-day refunds for any reason. With GlassesUSA and EyeBuyDirect, it’s within 14 days. Zenni Optical gives full store credit but only a 50% refund. There may be restocking fees, limits on the number of free exchanges and more.

If your online eyeglasses aren’t perfect, take them to a local optician for an adjustment. Again—expect to pay for the service, and it’s your risk if the frame breaks. Note: Warby Parker has some physical stores, but the location may be inconvenient for multiple ­adjustments.