Vision should be measured by a professional, as over-the-counter lenses can be inaccurate and potentially weaken the visual system.

“The ones that you get in those supermarkets, or in many eyeglass stores, apologies to the eyeglass stores, are often wrong by an order of magnitude. And then, when you start putting corrective lenses on that are over-correcting or under-correcting, but more often are over-correcting, well, then you're essentially weakening the system.”