Prism trial frame 1910
This is a very rare trial frame. The holders are rectangular in order to hold old style rectangular prisms.
According to Spectacles and Other Vision Aids , by Rosenthal, this very rare prism trial frame was manufactured by American Optical Co. in 1910. Its purpose is to hold prisms in the course of determining of what amount and in what direction prisms should be used on a given patient.
The prism trial frame has a nasal, temporal and inferior guard with one groove. (meaning each side could hold one prism).
In addition, there is a temporal spring clip to secure the prism into place once placed in the trial frame.
This prism trial frame is not marked or signed.
Today’s trial frames use round prism lenses which fit the grooves in the trial frame just like the spherical and cylindric lenses. So there is no need for a special prism trial frame which only accepts rectangular prisms.
