From Joe Oldaker, Nuneaton, Warwickshire, UK
Agatha Windig is probably on to something with her observation that contact lenses stop the tears while chopping onions, but not that it involves the iris and pupil. A rigid gas-permeable lens would probably filter out the volatiles that the onions release, keeping them from irritating the surface of the eye, the cornea, which would prevent tears. The iris and pupil wouldn’t be involved, as such – the iris is an internal structure and the pupil is an aperture in it(Letters, 12 July).
