EP1773181A1

EP1773181A1 - System for wave front measurement

Info

Publication number: EP1773181A1
Application number: EP05778347A
Authority: EP
Inventors: Michael Mrochen; Markus Meier
Original assignee: IROC AG
Current assignee: IROC AG
Priority date: 2004-08-03
Filing date: 2005-08-02
Publication date: 2007-04-18
Also published as: DE102004037558A1; WO2006015770A1

Abstract

The invention relates to a system for wave front measurement, said system comprising a wave front sensor (18) and a compensator (14) for pre-compensating optical imaging errors of radiation oriented into the wave front sensor. According to said system, the compensator (14) for pre-compensating higher order optical imaging errors comprises transmitting optical elements, and means (20) are provided for displacing at least one of the optical elements for adjusting the pre-compensation.

Description

Wavefront detection system

The invention relates to a system for frontal wavefront measurement with a wavefront sensor and a compensator for precompensation of optical aberrations of the radiation to be measured by the wavefront sensor.

In ophthalmology, optical aberrations of the prior art eye are measured with wavefront sensors. In particular, wavefront sensors according to Shack-Hartmann and Tscherning are known. Such micrometers permit the measurement of optical properties of the entire "eye" system and serve, in particular, as a basis for refractive surgical interventions, for example with the laser according to the LASIK method can serve both for diagnostic and therapeutic purposes in ophthalmology.

The state of the art already knows a so-called NulP measurement in front-of-line measurement, in which a large part of the aberrations of the eye are precompensated before the frontal measurement. In this case, the precompensated error is known and the remaining error measured in the wavefront sensor can then be determined with much higher accuracy, because the so-called dynamic range of the wavefront sensor, ie the permissible distance between the maximum and minimum values, is greatly expanded. The state of the art knows about the precompensation of optical errors, such as defocus and astigmatism, movable telescopes (Badal optometers) and even crossed cylindrical lenses. If, in addition, optical aberrations of a higher order, for example the spherical aberration, are to be compensated in terms of time, then in the prior art this is done only via adaptive mirror systems which reflect the radiation. A temporal compensation be¬ is also referred to as "closed loop ^w system, if a continuous measurement of optical Wellenfrontfehlem and their continuous compensation by geometrical changes to see carried out an adaptive mirror. US patent application US 2003/0193647 A1 shows a system in which exclusively a telescope is used for the compensation of defocus errors in a closed loop; a compensation of spherical aberration or coma is not shown.

US 2004/0041978 A1 also shows a system with a telescope which uses a spatial filter to eliminate the higher-order optical aberrations in a wavefront measured at the wavefront sensor. An optical spatial filter does not compensate for optical aberrations, it just filters them. One can therefore understand this prior art as a low-pass filter in which the aberrations higher order are cut off.

The present invention has for its object to provide a system for wavefront measurement, in particular, higher-order aberrations in a simple manner and with high reliability can be precompensated to improve the dynamic range of the wavefront sensor used.

For this purpose, the invention provides a system for wavefront measurement comprising a wavefront sensor and a compensator for precompensation of optical aberrations of radiation directed into the wavefront sensor, wherein the compensator has optical elements transmitting precompensation of higher order optical aberrations and means are provided, to move at least one of the optical elements to adjust the pre-compensation.

A "higher-order optical aberration" is to be understood here in particular as an aberration of the third order and a higher order (coma-like aberration)., In particular, aberrations of the fourth order are also referred to as "optical aberrations of a higher order" to understand the present invention, ie spherical aberrations. A transmitting optical element in this sense transmits the electromagnetic radiation and thus has a refractive effect for this radiation. The invention is based on the finding that with transmitted optical elements the above-stated object can be achieved in an advantageous manner and the dynamic range of the wavefront sensor can be maximized with regard to certain selected optical aberrations, for example of an eye.

According to the invention, therefore, previously calculated lenses are used which have a defined order of magnitude of spherical aberration. By selecting specific combinations of the respective spherical aberrations in the different optical elements, the sum (at the measuring sensor) results in a superposition of the optical errors. By shifting the optical elements relative to one another, it is now possible to set specific values of, for example, spherical aberration or coma.

According to a preferred development of the invention, it is provided that the means for moving at least one of the optical elements receive signals from the wavefront sensor in order to move the optical element as a function of the signal. In this variant of the invention, the precompensation can be selectively optimized, in particular with regard to the optical error of higher order to be pre-compensated and the improvement of the dynamic range with respect to certain optical aberrations to be gained thereby. The precompensator also compensates for low-order optical errors in a known manner.

Another preferred embodiment of the invention provides means for displaying data corresponding to the precompensated wavefront so that a physician receives information about the precompensation during the wavefront measurement and, if desired, could intervene selectively. It is also possible to perform the precompensation without the static feedback described above in accordance with predetermined optical errors that are to be compensated.

The means for displaying the pre-compensated wavefront may also serve for a functional eye vision check of the eye.

The wavefront error of the eye which is ultimately to be measured then results from the wavefront measurement carried out after the precompensation, taking into account the precompensated error which is to be added to the result of the wavefront measurement.

Exemplary embodiments of the invention will be explained in greater detail below with reference to the drawing. It shows:

FIG. 1 schematically shows a system for wavefront measurement with precompensation;

FIG. 2 shows another system for wavefront measurement with precompensation using a Cherning aberrometer;

FIGS. 3, 4 show details of a compensator for the precompensation; and

FIG. 5 shows a system for wavefront measurement with display devices.

FIG. 1 shows schematically the radiation course and the processing of the radiation. A Shack-Hartmann sensor for wavefront measurement, which is well known to the person skilled in the art, is used. The illustration in FIG. 1 begins with the "eye" optical system 10. The measuring beam directed to the eye and its shaping are sufficiently known as such and omitted from FIG optical aberration (aberrations) of the eye, ie in particular the knew aberrations simpler and higher order. A typical higher-order aberration is known to be the spherical aberration. This radiation from the eye is input to an optical system 12, for example a telescope. Thereafter, the radiation enters a compensator 14, which precompensates the wave front. This compensator 14 has transmitting optical elements in the above sense, ie the elements transmitting and refracting radiation, which are shown by way of example in FIGS. 3 and 4. The compensator 14 performs a pre-compensation of higher-order optical errors.

After precompensation in the compensator 14, the radiation passes through an optical system 16, with which it is imaged onto a wavefront sensor 18. The wavefront sensor 18 enables a wavefront measurement with the features and advantages described above. With the components described above, the system first of all enables static precompensation with a predefinable optical error which is to be compensated. The compensator 14 has movable trans¬ mittierende optical elements (Figure 3, 4), which are movable by means of a controller 20.

According to a particular embodiment, which is likewise shown in FIG. 1, the measurement result is fed back from the wavefront sensor 18 to the compensator 14 by means of the control electronics 20. The individual transmitting optical elements of the compensator 14 can then be dependent on the measurement signal of the wavefront sensor 18 optionally be set so that the Dynamik¬ range in the wavefront sensor 18 can be maximized in terms of particularly interesting higher order error.

FIG. 2 shows a system for wavefront measurement using a Chering Aberrometer. Here as well, as in FIG. 1, the components for generating and shaping and guiding the laser beam with which the measurement is carried out have been omitted. The illustration in FIG. 2 begins with the mask system 22 for generating a dot pattern with which the optical aberrations of the eye in FIG known manner to Cherning be measured. The dot pattern is imaged via an optical system 24, for example a telescope, into a wavefront compensator 26, of which exemplary embodiments are illustrated in FIGS. 3 and 4. The compensator 26 thus again has transmitting optical elements. The radiation coming from the compensator 26 is imaged onto the retina of the eye 30 via imaging optics 28. This image is imaged in a manner known per se in the wavefront sensor 32, ie in this case the Cherning aberrometer, for measuring the point shifts.

The wavefront compensator 26 is controlled with its individual components by means of a controller 34 in such a way that the desired precompensation takes place. According to an expanded embodiment, a feedback from the wavefront sensor 32 to the wavefront compensator 26 is provided, with control electronics 34 receiving signals from the wavefront sensor 32 in order to control the elements of the compensator 26 to achieve a desired precompensation in accordance with these signals.

The mitteis the compensators 14 and 26 to be performed precompensation can be, for example, a spherical aberration, a coma or an astigmatism.

Details of the compensators 14 and 26 are shown in Figures 3 and 4. The construction as such is known from Buchroeder and Hooker, Applied Optics, 14, 2476, 2469 (1975). The lens system according to FIG. 3 is an afocal telescopic Galileo system. After the lens 4, the beam path is parallel and is focused by the lens 5 on the image plane. The first lens 1 is spherically strongly overcorrecting. The lens 4 of the telescopic system is spherically corrected. The adjustment (control) of, for example, spherical aberration occurs in the lens group 2/3. This lens group has virtually no refractive power, but a strong spherical undercorrection by the lens 2. By shifting in the z-direction (ie in the direction of the laser beam) can be a desired spherical A- berration with either (depending on the direction of displacement) positive or negative - characters are generated. The lens group 2/3 can also be used to adjust a coma. For this purpose, it is moved in the xy plane (perpendicular to the paper plane). Two elements compensating for spherical aberration produce a coma during lateral displacement (see Lopez, "Generation of third-order spherical and aberrations by use of symmetrical four-order lenses", JOSA A, 15, 2563-2571 (1998)).

Astigmatism can be generated with the optical system according to FIG. 3, for example by tilting the lens 5. This is indicated by the curved arrow in FIG.

FIG. 4 accordingly shows a lateral displacement of the lenses 2/3 for generating coma, wherein at the same time the lens 5 is tilted with respect to the optical axis to produce astigmatism.

Commercially available achromatic lens systems are corrected for spherical aberration and Ko ma, but they can not be corrected for astigmatism. This can be exploited for the purposes of the present invention. Since the image field curvature is likewise not corrected in the case of an achromatic image, the image plane is suitably curved so that it lies between the tangential and sagittal image surface.

In this way it is possible, in particular, to generate the following monochromatic wavefront aberrations: spherical aberration, coma, defocus and astigmatism.

It is also possible to correct chromatic aberrations (dispersion). In the systems according to FIGS. 3 and 4, it would be expected that due to the use of single-cell lenses no color correction would be possible. This is particularly important in examining the eyesight of the optical system. In the example given here, the two achromatic lenses 4 and 5 are color-corrected for visible light. However, because they are used in the embodiment with light of a wavelength of 785 nm, they are chromatically undercorrected. The chromatic effect (s) of the lens 1 on the one side, and the lenses 4 and 5 on the other hand, however, lead to a rather good chromatic correction of the overall system (minimization of chromatic errors).

The lens systems illustrated in FIGS. 3 and 4 allow, for example, a static, i. fixed predetermined control of the wavefront aberration with the mechanical assemblies not shown in detail for example, a linear movement for Er¬ generation of the spherical aberration and the coma, or for a rotation to produce the astigmatism. It is also possible to generate the desired wavefront aberration dynamically by means of a feedback control loop, as described with reference to FIGS. 1 and 2.

Typical values for the lenses used are: lens (1) focal length f = -24 mm with a greatly overcorrected spherical aberration and negative dispersion; Lens (2) focal length f = + 40mm with a strongly undercorrected spherical aberration and positive dispersion; Lens (3) focal length f = -40 mm with negative dispersion.

The optical elements according to FIGS. 3 and 4 thus make it possible to correct the dispersion (of the chromatic aberration) of the optical compensator.

FIG. 5 shows a further exemplary embodiment of a system for wavefront measurement, in which the components corresponding to the exemplary embodiment according to FIG. 1 are provided with the same reference numerals, supplemented by a dash. In that regard, reference is made to the above description. In addition, in the system according to FIG. 5, information about the precompensated wavefront is displayed to the treating physician in a display device 40. The optical elements according to FIGS. 3 and 4 can be arranged so that the examined eye can see through it. This can be used for eye tests. It is also possible to connect to the display devices 40 or 42 of Figure 5, an optical system to compensate for possible magnification errors due to the compensator 14 '. In this case, the magnifying optical system can also serve to carry out functional tests of the eyesight of the examined eye.

Claims

claims

1. System for wavefront measurement with a wavefront sensor (10; 32) and a compensator (14; 26) for pre-compensation of optical aberrations

5 of radiation directed into the wavefront sensor, characterized in that the compensator (14; 26) has at least two transmitting optical elements (1, 2, 3, 4, 5) for precompensation of higher order optical aberrations and that means (20; 34) are provided to move at least one of the optical elements for setting the pre-compensation lo.

2. System for wavefront measurement according to claim 1, with at least one transmitting optical element (1) which is centered to the optical axis and spherically overcorrected or undercorrected, at least one further transmitting optical element (2/3) which is overcorrected spherically or is undercorrected, and with at least one further transmitting optical element (4) which is spherically overcorrected or undercorrected, wherein

Means (20; 34) are provided for moving at least one of the optical elements to adjust the precompensation.

3. System according to claim 2, wherein the compensator (14; 26) for precompensation of optical aberrations of higher order is provided with at least one additional transmitting optical element (5), wherein the

25 ses optical element by tilting to the optical axis generates an astigmatism and wherein means (20; 34) are provided to move these optical elements for setting the pre-compensation.

4. System according to claim 1, 2 or 3, characterized in that the means

30 (20; 34) for moving at least one of the optical elements (1, 2, 3, 4, 5) Receive signals from the wavefront sensor (18; 32) to move the optical element in response to the signal.

5. System according to one of the preceding claims, characterized by means

5 (40, 42) for indicating the precompensated wavefront, respectively

Dates.

6. System according to any one of the preceding claims, characterized in that it is designed for ophthalmic wavefront measurement.

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7. System according to one of the preceding claims, characterized in that it is color-corrected for the visible region of the eye 350 nm to 850 nm.

8. System according to one of the preceding claims, characterized in that it is designed for a visual examination on the human eye.

9. Use of a system according to one of the preceding claims for a wavefront measurement on the eye.

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