Patent GB-431705-A (GB)
Title: Improvements in eye testing method and apparatus therefor
IPC: A61B3/02
Filed: 1934-01-15
Abstract: 431,705. Sight-testing apparatus. BROOKES, N. E., 1, Quality Court, Chancery Lane, London.-(Dartmouth College, Trustees of; Hanover, New Hampshire, U.S.A.) Jan. 15, 1934, No. 1434. [Class 97 (i)] Apparatus for sight-testing, particularly for detecting differences between the sizes or shapes of the two separate ocular images formed by a person's two eyes, comprises means for presenting superimposed images of two charts or targets in such a way that the patient observes one image with the right eye only, and the other image with the left eye only, these charts bearing test objects or marks of identical form which can be fused into a single image, and also bearing additional marks having, on each target, the same positional relationship to the fusible object. These additional marks are of dissimilar form or appearance on the two targets so that they cannot be fused together by the eyes, and the image differences referred to above are evaluated by determining the apparent positional differences between corresponding marks on the two targets. The apparatus also includes means for testing for ordinary refractive defects, and for phoria &c. Fig. 1 shows diagrammatically the manner in which the test is carried out. Images of the targets X, Y are presented to the left eye OS and the right eye OD respectively by means of transparent mirrors M, M<1>, the lines of sight being arranged to converge either at a far point F in the horizontal plane of the eyes, or at a near point E in a downwardly-inclined plane. The targets bear identical marks in the form of central rings X<1>, Y<1>, the images of which are fused by the patient's eyes, and also carry additional marks comprising, on the disc X, a number of black dots 11 .. 41 and, on the disc Y, a number of apertures 1<11> .. 4<11> which are illuminated from the rear. The patient thus sees dark images of the points 11 .. 4<1> and bright images of the points 1<11> .. 4<11>, so that visual defects of the kind above mentioned can be detected by the apparent differences in position of the images of corresponding points on the two targets. These defects may be corrected by inserting lenses of the kind described in Specification 412,081 between the eyes and the mirrors M, M<1>, or their magnitudes may be determined by making one or both of the targets adjustable to obtain coincidence of the images. For example, the target X may be rotatable about the axis m and displaceable along, and at right-angles to, this axis and each of the marks 11 .. 41 may be radially adjustable on the target. Instead of using two separate targets of which virtual images are presented to the eyes, a single directly viewed target may be used consisting of a screen A having a central aperture F surrounded by small apertures 1 .. 4. Behind the screen A is a screen B with apertures 31, 32, &c., Fig. 4, corresponding to the apertures 2, 4, &c., and provided with opaque shutters 33, 34 half covering the apertures 31, 32. The screen B is illuminated from the rear so that, as seen in Fig. 4, the left eye sees the apertures 1 .. 4 as bright spots and the right eye as dark spots. The shutters 33, 34 may be slidably arranged so that bright images can be presented to either eye. The fields of vision of the eyes may be restricted by screens 25, 26 to reduce the patient's depth perception. The patient's head is accurately positioned by means of a universally-adjustable head rest 10. Refractive defects are estimated by the use of a focusing object which is moved to and fro along the line of vision until it is sharply focused by the eye. These focusing objects may be positioned as at O, O <1>, Fig. 1, so that their virtual images formed by the mirrors M, M<1> are observed, or they may be arranged directly on the lines of vision as at R (for distant vision) and P (for near vision), the light from the focusing objects passing through the central apertures in the targets X, Y, or through those in the screens A, B. The construction of an apparatus for testing in the above manner is fully described in the Specification.