Steinhuber W
Klin Monbl Augenheilkd. 1985 Nov;187(5):385-6. doi: 10.1055/s-2008-1054341.
A beam splitter on a phoropter permits fixation of optotypes while retinoscopy is being performed. The eye being examined can see the optotypes in the focus of a lens or on the wall behind the examiner by means of a periscope system. The great distance of the retinoscopic lens from the eye increases the retinoscopic phenomenon.