To be fashionable, and possibly improve vision at the same time, the pince nez style of glasses became popular. The 'Fits-u' design has a mounting that allowed the bridge to stay solid, whilst the springs in the nose pads allowed for removal (unlike pince nez which had a springs in the bridge). Although complete, this box includes models with different distance dimensions and the height of the bridge, with these figures are etched onto the lenses. An order table is included in the box with the pupillary distance and height so the catalogue number and quality and quantity of each size can be ordered by the dispenser. The pupillary distance is used to design spectacle frames.Canvas box which includes display models of different dimensions of pince nez Handwritten on the back: James Korp Backhouse (?) 1904 Ophthalmic Optician & Optometristassistive devices, american optical company

How widely the prisoptometer was used is unclear but the Standard Optical Company later patented a new model, The Standard Prisoptometer, on June 21, 1904. Edward Jackson's crossed cylinder technique of determining astigmatism was first detailed in the Transactions of the American Ophthalmological Society (1887)4:595-598. The convenience of Jackson's crossed cylinder lenses over the prisoptometer in weight, cost, portability and reliability meant that they were soon almost universally adopted.This is a rare item as few are known world wide.This instrument is an optometer, that is, a device to measure the refractive error of an eye. It is made of cast iron, steel, brass and glass. It contains a prism which could be rotated, and was used to view a disc or an object circle. The prism caused monocular doubling of the object circle and the separation of the two images varied as the prism rotated, depending on the astigmatism present. The axis of the astigmatism was indicated by the prisoptometer and trial lenses were used to determine the the magnitude of the spherical and cylindrical refractive errorImprinted:"DR CULBERTSON'S PRISOPTOMETER/ GENEVA OPTICAL COMPANY MAKERS, GENEVA, N.Y./ PATENTED SEPT, 21, 1886". Stamped "853" on eyepiece and lens mounting.optometry, prisoptometer, optometer, astigmatism, refractive error, refraction, culbertson