Halberg clip

clip, Halberg 

Trade name for a plastic device with two cells used for holding trial lenses which is clipped over a lens of a pair of spectacles (Fig. C12).
Fig. C12 Halberg clipenlarge picture
Fig. C12 Halberg clip
Millodot: Dictionary of Optometry and Visual Science, 7th edition. © 2009 Butterworth-Heinemann