If you have been wearing glasses for years, like me, it can be surprising to discover that you perceive the world thanks to a few giant companies that you have never heard of. Worrying about the fraying edge of motorway lights at night, or words that slide on the page, and occasionally spending a fortune at the opticians is, for many of us, enough to think about. And spectacles are unusual things. It is hard to think of another object in our society which is both a medical device that you don’t want and a fashion accessory which you do. Buying them, in my experience anyway, is a fraught, somewhat exciting exercise that starts in a darkened room, where you contemplate the blurred letters and the degeneration of your visual cortex, and ends in a bright, gallery-like space where you enjoy the spry feel of acetate in your fingers, listen to what you are told, pay more than you were expecting to, and look forward to inhabiting a new, slightly sharper version of your existing self. The $100bn (£74bn) eye wear industry is built on feelings such as this. In the trade, the choreography that takes you from the consulting room to the enticing, bare-brick display of £200 frames is known as “romancing the product”. The number of eye tests that turn into sales is the “capture rate”, which most opticians in Britain (or optometrists, as they are known in the rest of the world) set at around 60%.