Patent GB-1303691-A (GB)
IPC: G03B35/10
Filed: 1970-07-08
Abstract: 1303691 Stereo ophthalmoscope-camera J H McMILLIN 8 July 1970 33170/70 Headings G2A and G2J A combined stereo ophthalmoscope and camera can be used for either observing or photographing the fundus of the eye. The device is adjustably mounted on the verticle post 36 of a stand 34, and comprises a base 40 which carries the camera structure. This includes a fixed optical unit 26 and a movable optical unit 30, the latter being carried by a camera housing section 32 mounted on a dove-tail slide so that it can be adjusted in the axial direction for focusing purposes by rack- and-pinion means operated by a focusing knob (108), Fig. 5 (now shown). In using the device, a speculum, curved so as to fit under the eyelid and against the sclera of the eye, is placed in position, the speculum having an apertured recess in which the nose of the camera is located. In the nose of the camera is mounted a masking disc 94, which has a lower aperture 92 see also, Fig. 6 (not shown) and two upper apertures (98). The eye is illuminated by means of a lamp 60 mounted in the lower part 62 of a lamp housing 74. Light from lamp 60 passes through a condenser lens 58 and is reflected from a mirror 86 through an objective lens system 90 and aperture 92 into the eye. Light reflected from the fundus passes through the upper apertures (98) in disc 94 and enters the stereo optical system 28, shown in more detail in Fig. 1. This comprises a pair of oppositely inclined rhomboidal prisms 114, which reflect the two ray pencils through a pair of triple-element objectives 116, this part of the system forming the fixed unit 26. The rays then enter the movable unit 30, which has a pair of image-erecting sub-systems 124, each comprising a field lens 126, a rhomboidal prism 128, and a triple-element lens 130. The rays are now reflected vertically upwards by a pair of stationary mirrors 138, and may be reflected by a further mirror 172 to the two eyepiece lenses 186. The device is now acting as an ophthalmoscope, and in the focal plane of each lens 186 is mounted a fixation target plate 214 having at its intersection with the optical axis, an indentation or mark to act as a fixation target for the person under examination. Below each target plate is a passageway 218 leading to a bore containing a miniature lamp 220 energised from batteries housed within the device, for the purpose of illuminating the target plate. The mirror 172 can pivot about an axis 170, and when it is swung down into the position shown in broken lines, the light reflected upwards from mirrors 138 can pass directly to the photographic film 142. It reaches the film by way of two circular apertures 308 in the top wall 306 of the camera housing seen more clearly in Fig. 11 (not shown). These apertures are spaced apart the same distance as the mirrors 138, so that a pair of stereoscopic images are produced on the film 142. The light source for the photographic exposure is a flash bulb 52 mounted in the upper part of the lamp housing 74. Both lamps 60 and 52 are energised from a low voltage source such as the low voltage winding of a step-down transformer. In operating the device, a cocking arm (286), Fig.12 (not shown) is pushed downwards, which brings the mirror 172 up into the full-line position of Fig.3, at the same time tensioning a driving spring, the mirror then latching in this position. The device is then placed in position with regard to the eye, as described above Fig. 14 (not shown), and the focus adjusted so that a clear sharp image of the fundus is obtained. A release lever (292) is now actuated, which releases the driving spring, thus causing mirror 172 to swing downwards. In so doing, it unblocks the path to the film 142 and at the same time engages an arm 237 of a microswitch 239, which closes a circuit to fire the flash bulb 52.