The Busch-Thorner optometer (Thorner's eye refractometer)

Historical Significance: United States Patent 3634003 for an OPTICAL SYSTEM FOR IMAGING SCHEINER APERTURES IN AN OPTOMETER was issued to Walther Thorner in July 1917 - 1235170 indicating that this instrument was devised in or before 1917. There are a number of papers in the literature reporting it or its use in investigations in the late 1920s. eg an exhibit of it by Emil Busch Optical Co., Ltd. reported in Trans. Opt. Soc. 1929; 31: 40 doi: 10.1088/1475-4878/31/1/305 and one in Scandinavica Acta Ophthalmologica 1928; 6:1-4. Judging by the cover photograph the booklet is likely to date in the 1930s. It has also been used in more modern investigations (eg Le Grand and El Hage, 1980, J Pujol, J Gispets, M Arjona 2003. The patent identifies Thorner as a subject of the King of Prussia living in Berlin. The patent describes it 'In an optometer of the type employing Scheiner apertures, an optical system is disclosed for projecting those apertures into a plane proximate to the eye, most commonly the plane of the pupil. According to the arrangement of the system, the plane of projection of the apertures and the plane of refraction, that is, the vertex distance of refraction, are separable.' It seems that the Fincham coincidence optometer (See Cat No 629) may be a development of the Thorner optometer. See Fincham The coincidence optometer. Proc Phys Soc 1937