Warby Parker, the company that sells eyeglasses by mail, has created an app that can check your prescription online. The app is called Prescription Check. It doesn't work for reading, progressive, or bifocal lenses — it only will test distance.
If you live in one of the states that will allow this, and you're between 18 and 50, you can try this. You just place your computer on a flat surface, then link it to your iPhone, hold up a credit card to the computer screen (to allow it to figure out how big the computer screen is), then walk backward while keeping the iPhone camera pointed at the computer screen. It will know how far away you are, and tell you when you're the required distance for the test. Then you can take a 20 minute vision test on your computer. The test costs $40.
Find out more about the Prescription Check app at warbyparker.com.