The drawbacks of common spectacles—the difficulty of correcting ametropia of the moving eye, the diminishing or magnifying effect of the spectacles, according to their distance from the eye, the frequent impossibility of wearing glasses of high power, the unsatisfactory cosmetic effect and their troublesomeness in some occupations—of necessity led, long ago, to the fundamental idea of the so-called contact glasses. These shell-shaped glasses are made up of two main portions, viz., the central corneal one for the correction of ametropia and the peripheral scleral one, which provides for the proper fitting of the glasses. The corneal portion of the contact glass represents in the air an afocal, i. e., a nonrefringent, optic system. When the contact glass is put on the eyeball, there collects—however closely the glasses may be fitted—a film of lacrimal fluid between the anterior surface of the natural cornea and the posterior face of