1,264,249. Tonometers. AMERICAN OPTICAL CORP. 9 Dec., 1969 [8 Jan., 1969], No. 60008/69. Heading ASK. [Also in Division G2] In an applanation tonometer, a contact element 10 (Fig. 1) is viewed through a stereomicroscope 2 and a biprism 24 (Fig. 3) is placed at the entrance pupil in order to produce two images of the contact area. The biprism is mounted on a plate 18 with its apex passing through the axes of two of four apertures 20 in the plate 18, and the plate is fixed to a flange 16 to form an assembly 14 which may be fitted onto, and rotated relative to, the objective 6. A partial reflector 8 is used to reflect illumination light towards the eye 12.
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