Optics: eye examining – vision testing and correcting – Eye examining or testing instrument – Objective type
Patent
1983-10-07
1987-01-20
Bovernick, Rodney B.
Optics: eye examining, vision testing and correcting
Eye examining or testing instrument
Objective type
351205, 351214, A61B 310
Patent
active
046377000
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a method and an apparatus for determining the refraction of the human eye, The invention relates specifically to a method for determining refraction as a fraction of time. In accordance with the invention an object in the object space is imaged by means of an optometer lense system onto the retina of the eye. The retinal image of said object, in turn, is imaged back via said optometer lense into the object space into a certain image plane, the image plane being conjugated to the retina and being defined by the status of refraction of the eye and the refracting power of the optometer lense; the distance of said image plane from said optometer lense being representative of the status of refraction, and wherein according to the invention for determining said distance the beam of rays coming from said retinal image is analysed at locations having different distances with respect to said image plane.
Automatic methods for determining the refraction are known (see FIG. 1). According to said known methods image plane conjugated with respect to the retina of the tested eye is detected. The methods known from German Auslegeschrifts Nos. 29 37 891, 31 10 576, 31 02 450 provide for the imaging onto the retina of an object, which may have the form of a grating, a point, or a slit, by means of an optometer lense system.
The retinal image is reflected back (as a reflected image) into the object space by means of the optometer lense and a beam split mirror (beam splitter). Said reflected image is analysed in the object space by means of another target object. For the purposes of said analysis the luminous flux which is transmitted by said target object is determined by a photosensitive element. It is therefore necessary that both objects correspond to each other as far as shape and dimension are concerned. So as to detect the conjugated image plane, the two objects are moved together with the beam splitter along the optical axis, or, according to a different method, the refracting power of the optometer lense system is varied. As soon as the position of the conjugated plane is found, a maximum, or depending on the kind of arrangement used, a minimum, of the luminous flux is measured behind the target object by means of the photo sensitive element. The refracting power of the eye is not supposed to vary during said movement. With such a method the variation of the refracting power of the eye as a fraction of time can not be determined without difficulties.
German Auslegeschrift 22 62 886 provides for an improvement by periodically moving the object system at high frequency for only a small distance along the optical axis. The result is a periodic change of the photo signal synchronous to said periodic movement. From the phase shift between the movement of the object system and the photo signal an electrical photo signal may be derived for a sufficiently high oscillation frequency. The photo signal indicates which direction the object system has to be moved so as to have the conjugated plane in the center between the points of reversal of the periodic movement. This method has the disadvantage that high mechanical oscillatory frequencies are required, i.e. high values for acceleration are necessary. Moreover, the determination of the phase is difficult because of the low signal
oise-ratio of the photo signal.
The method of German Auslegeschrift 26 54 608 provides for a certain improvement with regard to the mechanical oscillations. Said known method replaces the continuous oscillation by a measurement only at two locations. However, even with this method the signal necessary for controlling the movement of the object system along the optical axis has to be derived indirectly from the phase relation between the physical position and the photo signal.
Another principal method for automatically determining refraction is the method of skiascopy, described below.
It is an object of the present invention to avoid the disadvantages of the prior art.
A specific object of the invention is to provide a meth
REFERENCES:
patent: 3791719 (1974-02-01), Kratzer et al.
patent: 4079248 (1978-03-01), Lehureau
Cornsweet et al., Journal of Optical Society of America, Apr. 1970, vol. 60, pp. 549,550.
Bovernick Rodney B.
Dzierznski P. M.
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