Optics: eye examining – vision testing and correcting – Eye examining or testing instrument – Objective type
Patent
1990-07-02
1993-03-30
Bovernick, Rodney B.
Optics: eye examining, vision testing and correcting
Eye examining or testing instrument
Objective type
351205, 351237, A61B 310, A61B 302
Patent
active
051988453
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
1. Technical Field
The present invention relates to an apparatus for producing an image of an object and, in particular, for examining the eye.
2. State of the Art
The difficulty in examining the posterior portion of the eye is that the illumination and the examination have to be conducted through the pupil and the optically often not clear anterior media of the eye, in which reflexes occur and which cause aberrations.
For some time, therefore, it has been recommended to employ scanning devices that do not illuminate large areas of the posterior portion of the eye, but scan the posterior portion of the eye with as small as possible an illumination beam and note the reflected light in correlation to the scanning sequence instead of using conventional fundus cameras. Reference with regard to this is made, by way of illustration, to "The Foundations of Ophthalmology", Vol. 7, pp. 307/308, 1962, U.S. Pat. No. 4,213,678, Japanese patent publications 61-5730 and 50-138822 and EP-A-0145 563.
The state of the art devices for examining the eye therefore have a number of disadvantages:
By tilting the elements forming the scanning beam and the reflected light, respectively the scattered light beam toward each other and by deflecting the beam two-dimensionally, which is necessary for the x/y scanning motion, the scale of the imaging is not constant over the area of the image.
This results in a rectangle being distorted trapezoidally, which is particularly disturbing if, by way of illustration, an electronic image assessment of sequentially shot areas are to be "adjoined".
Description of the Invention
The object of the present invention is to further improve an apparatus for obtaining an image and, in particular, for examining the eye in such a manner that the trapezoidal distortion is conpensated for.
A solution to the aforegoing object and its further embodiments are set forth in the patent claims hereto.
In accordance with the present invention, the aforegoing object was solved by providing at least one aspherical element, which compensates for the trapezoidal distortion, in the beam path between the scanning elements and the object, of which the image is to be made.
One embodiment of the present invention is provided with an additional aspherical element, which bundles the image in the pupil plane of the eye; the first aspherical element then compensates for the trapezoidal distortion in the plane of the second element.
By way of illustration, in ophthalmological applications, the bundle of rays is usually bundled in the pupil of the eye. As this bundling of rays in the image of the pupil has to be taken into account, it is advantageous to provide a second aspherical element, which yields an additional degree of freedom in correction.
The first element brings about a distortion correction in the plane of the second element. The second element then ensures an exact bundling of rays in the image of the pupil.
If both the distortion correction in the image of the pupil and the bundling of rays in the pupil plane are fulfilled, the bundle of rays corrects the distortion in all other plane section images.
Furthermore, it is preferable if the refractive power of both aspherical elements is practically zero in the region of the optical axis.
BRIEF DESCRIPTION OF THE DRAWING
The present invention is made more apparent in the following section using a preferred embodiment with reference to the accompanying drawing, in which:
FIG. 1 depicts a section through a part of an invented apparatus, and
FIG. 2 schematically depicts a correction surface.
DESCRIPTION OF A PREFERRED EMBODIMENT
The invented apparatus illustrated in sections in FIG. 1 is provided with a not depicted illumination light source, by way of illustration a laser, and a not depicted detector device, the output signal of which is assessed by an evaluation and synchronization unit and, by way of illustration represented on a monitor. In the illustrated preferred embodiment both the illumination beam 14 and the light beam 15 coming from the fu
REFERENCES:
patent: 4447112 (1984-05-01), Matsuoka
patent: 4781453 (1988-11-01), Kobayashi
patent: 4838679 (1989-06-01), Bille
Bovernick Rodney B.
G. Rodenstock Instrument GmbH
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