GB687953A - Improvements relating to sight testing apparatus - Google Patents

Abstract

687,953. Sight-testing apparatus. ELLIMAN, H. May 7, 1951 [May 16, 1950], No. 12132/50. Class 97 (i). Sight-testing apparatus particularly for determining astigmatism comprises a chart presenting a substantially circular scale showing meridians, and meridian indicating means mounted concentrically with said scale and rotatable relative to the latter, said indicating means comprising at least four pointers of which no two are disposed parallel to a common meridian on the scale and of which not two are diametrically opposed. As shown in Fig. 3, the pointers 11 may be in the form of a series of antiguous black dots arranged tangentially to a circle concentric with the white rotatable disc 4 carrying the dots. Alternatively the pointers may be in the form of black lines arranged radially on the disc which also carries a black central spot 8. In the form shown in Fig. 5 the pointers 10 are in the form of a metallic spider having a central portion 9 attached to a shaft 14 rotatable in a casing 12 by a knob 28 through gearing 26, 25 and a chain 22. The spider rotates before a translucent panel 13 being a circular meridian scale 3 and illuminated by lamps within the casing, the latter also carrying a similarly illuminated panel 36 bearing a letter scale. The rotatable pointers are employed in the usual way, described in the Specification, to determine the patients' astigmatic errors and the necessary corrections therefor.