Or perhaps now you don't ...
This bizarre looking device has seen to seeing that unseeing people get to see again. It probably has done so for decades.
The Bausch and Lomb Green's Genothalmic Refractor was introduced in 1934 following a long design gestation from the original Clyde L. Hunsicker invention, the 'optometer'. It went on to enjoy four decades of unrivaled use as the 'gold standard' of professional eye care equipment. Even today they are still being used to good effect.
This old specimen has however been retired to live out its days as a store front prop in a Hutt Street photography studio. I find the link a bit tenuous but it sure looks good in the shop window.
I'd wager a small bet that most of you of a similar age have been seen to and seen through one of these beauties sometime in your life,
... so maybe you do after all.
Photo: Robert Rath, 'Lessons Learned', 1/125s f1.8 ISO100 50mm