You can actually get a remarkably accurate prescription with no feedback at all.[1] You've almost certainly done this before as part of an eye exam. (Look in th

You can actually get a remarkably accurate prescription with no feedback at all.[1] You've almost certainly done this before as part of an eye exam. (Look in this machine at the balloon.) The refraction portion of the eye exam is the least important one for medical reasons and the one that people think has the highest stakes (getting the right glasses.) The other parts of the eye exam (pressure testing, retinoscopy, etc.) are worth far more to your overall health. 1: https://en.wikipedia.org/wiki/Autorefractor https://en.wikipedia.org/wiki/Autorefractor