Refractometer for the automatic objective determination of the refractive condition of an eye

Claim 1

Refractometer for the automatic objective determination of the condition of refraction of an eye, in which a test mark is focused by an optical image-producing system on the retina of the eye to be examined and the light reflected from the retina after passing through said image producing system and before reaching the test mark is reflected to a photoelectric receiver provided with a scanning device, characterized by the combination of the following features: (a) the image-producing system contains a first lens and a second lens between which there is a parallel beam path and which produce a first intermediate image of the test mark, as well as a third lens which, in combination with the eye lens, produces a second intermediate image of the test mark on the retina of the eye; (b) between the first and second lenses a partially transmitting mirror is arranged and, in the light-path of the latter, a lens corresponding to the first lens of the image producing system in such a manner that the light reflected by the retina produces a third intermediate image of the test mark outside the path of the illumination beam; (c) at the location of this third intermediate image there is provided a scanning device which, together with a photoelectric receiver arranged behind it, produces a signal which is modulated in accordance with the position of the intermediate image; (d) behind the photoelectric receiver there is provided an arrangement which converts the modulator signal into a control signal which is proportional to the deviation of the third intermediate image from the theoretical desired position; (e) one the lenses of the image producing system is displaceable by means of a motor (22) to which the control signal is fed.

Claim 15

The method of automatically determining the refractive condition of an eye, which comprises producing a first intermediate image of a test mark by means of spaced first and second lenses which establish a parallel-beam path therebetween, producing a second intermediate image of the test mark on the retina of the eye by means of a third lens and the lens of the eye, producing a third intermediate image of the test mark by means of a fourth lens outside the light path between the test mark and the eye and by partially reflecting retina-reflected light to the fourth lens, the partial reflection being from within the parallel-beam path between the first and second lenses, photoeletrically producing a signal which is modulated in accordance with the instantaneous position of the third intermediate image, converting the modulated signal to a control signal which is proportional to the deviation of the third intermediate image from its theoretical desired position, and using the control signal to axially displace one of the first three lenses in the direction which reduces the modulating signal.

Claim 16

The method of automatically determining the refractive condition of an eye, which comprises producing a first intermediate image of a test mark by means of spaced first and second lenses which establish a parallel-beam path therebetween, producing a second intermediate image of the test mark on the retina of the eye by means of a third lens and the lens of the eye, producing a third intermediate image of the test mark by means of a fourth lens outside the light path between the test mark and the eye and by partially reflecting retina-reflected light to the fourth lens, the partial reflection being from within the parallel-beam path between the first and second lenses, photoeletrically producing a signal which is modulated in accordance with the instantaneous position of the third intermediate image, converting the modulated signal to a control signal which is proportional to the deviation of the third intermediate image from its theoretical desired position, and using the control signal to axially displace one of the first three lenses in the direction which reduces the modulating signal.