A curious optical instrument has been invented by M. Houdin in France. It is termed as iridiscope and has for its object the detection of diseased conditions of the humors of the eye. It consists simply of a concave shell, having a small aperture in its center. The patient uses the iridoscope in the following manner: the instrument being placed upon the eye, he looks through the aperture at diffused light, and if the humors of the eye be altered in character, minute particles will be seen floating in the field of vision. M. Houdin says its principle is something like that upon which a water carafe is held up to the light to detect whether the contents are pure.
Diseased Humors of the Eye. Arch Ophthalmol. 2007;125(6):857. doi:10.1001/archopht.125.6.857-a