US 20050105044 A1
Wavefront measuring systems and methods are disclosed which may be employed, for example, in detecting phase aberrations in a spectacle lens and in an eye. Various embodiments include disposing a modulation pattern in the path of a return beam from the spectacle lens or the eye, and imaging a diffraction pattern at a self-imaging plane relative to the modulation pattern with a detector. The diffraction pattern is analyzed and the results are used to produce a representation of the wavefront phase characteristics that describe aberrations in the lens or eye being measured. Illumination and processing techniques for improving the measurement results are dislcosed. Various embodiments comprise systems adaptable to both measure aberrations in lenses in spectacles as well as in a patient's eyes.
1. A lensometer for measuring waveshaping properties of a corrective lens across at least a portion of the corrective lens, the lensometer comprising:
a light source for emitting light;
beam-tailoring optics that receives light from said light source and outputs a light beam having a beam size at least as large as said portion of said corrective lens to be measured, said light source, said beam-tailoring optics, and said corrective lens disposed along an optical path such that said light beam propagates through said corrective lens; and
a Talbot plane self-imaging wavefront sensor disposed in said optical path to receive said light beam after said beam has passed through said corrective lens, said Talbot plane self-imaging wavefront sensor configured for use in determining the waveshaping properties of the corrective lens.
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9. A method of measuring waveshaping properties of a corrective lens across at least a portion of the corrective lens, the method comprising:
propagating a beam through said corrective lens;
propagating said beam, having passed through said corrective lens, through at least one two-dimensional modulation pattern thereby producing a near field diffraction pattern at a Talbot plane;
imaging said near field diffraction pattern at said Talbot plane; and
determining a measure of said waveshaping properties of said corrective lens based at least in part on said near field diffraction pattern.
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propagating the beam through said corrective optics; and
reflecting the beam from a diffusely reflecting surface.
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25. A combination lensometer/ocular measurement system for measuring refractive properties of an object under test selected from the group comprising a corrective lens and an eye, said measurement system comprising:
a light source which emits a beam of light along a first optical path to said object under test;
beam-tailoring optics which alters one or more characteristics of the beam based on whether said object under test comprises a corrective lens or an eye;
a support structure for positioning said object under test in said beam for measurement; and
a wavefront sensor disposed to receive light from said object under test for measurement of optical wavefronts received therefrom.
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33. A method of measuring waveshaping properties of a wavefront, said method comprising:
propagating said wavefront through at least one two-dimensional modulation pattern thereby producing a self-image at a self-image plane of said two-dimensional modulation pattern;
forming an image of said self-image plane;
reducing contributions from portions of said image of said self-image plane based on comparisons of a characteristic of said portions of said image with a threshold; and
determining a measure of said wavefront based at least in part on said image of said self-image plane.
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This application claims the benefit of U.S. Provisional Application No. 60/520,294 entitled “Ophthalmic Diagnostic Instrument” (Attorney Docket No. OPH.024PR) filed Nov. 14, 2003, and U.S. Provisional Application No. 60/581,127, entitled “Lensometers and Wavefront Sensors and Methods of Measuring Aberration” filed Jun. 18, 2004, (Attorney Docket No. OPH.026PR), the entirety of which are incorporated herein by reference.
The invention relates generally to systems and methods for measuring wavefronts such as self-imaging based lensometers and wavefront sensors and methods of measuring aberrations of lenses such as corrective ophthalmic lenses as well as aberrations in the eye.
Traditional lensometers comprise an instrument used to determine the power and astigmatism (sphere and cylinder) of a spectacle lens. In particular, traditional lensometers comprise a centered telescopic optical system that includes a reticule and neutralizing lenses that can be employed to measure sphere and cylinder power as well as axis. A dial called the power drum is used in conjunction with an axis dial for introducing test correction such that lines in the reticule appear straight and in focus to the operator. Newer lensometer systems are automatic, however, these instruments still rely on the principle of neutralizing sphere and cylinder utilizing movable lenses.
Such conventional systems and techniques work adequately for lenses measuring sphere and cylinder. The measurement of sphere and cylinder of the spectacle lenses enables optometrists and ophthalmologists to provide conjugate correction for a near-sighted or a far-sighted patient who possibly has astigmatism as well. However, corrective optics provided on the basis of these sphere and cylinder measurements are often not suitable for correcting a person's vision. What is needed are improved systems and methods for measuring refraction of patients and for providing appropriate vision correction.
One embodiment of the invention comprises a lensometer for measuring waveshaping properties of a corrective lens across at least a portion of the corrective lens. This lensometer comprises a light source for emitting light, beam-tailoring optics, and a Talbot plane self-imaging wavefront sensor. The beam-tailoring optics receives light from the light source and outputs a light beam having a beam size at least as large as the portion of the corrective lens to be measured. The light source, the beam-tailoring optics, and the corrective lens are disposed along an optical path such that the light beam propagates through the corrective lens. The Talbot plane self-imaging wavefront sensor is disposed in the optical path to receive the light beam after the beam has passed through the corrective lens. The Talbot plane self-imaging wavefront sensor is configured for use in determining the waveshaping properties of the corrective lens.
Another embodiment of the invention comprises a method of measuring waveshaping properties of a corrective lens across at least a portion of the corrective lens. In this method, a beam is propagated through the corrective lens. The beam, having passed through the corrective lens, is propagated through at least one two-dimensional modulation pattern thereby producing a near field diffraction pattern at a Talbot plane. The near field diffraction pattern is imaged at the Talbot plane and a measure of the waveshaping properties of the corrective lens is determined based at least in part on the near field diffraction pattern.
Another embodiment of the invention comprises a combination lensometer/ocular measurement system for measuring refractive properties of an object under test selected from the group comprising a corrective lens and an eye. The measurement system comprises a light source, beam-tailoring optics, support structure, and a wavefront sensor. The light source emits a beam of light along a first optical path to the object under test. The beam-tailoring optics alters one or more characteristics of the beam based on whether the object under test comprises a corrective lens or an eye. The support structure positions the object under test in the beam for measurement and the wavefront sensor is disposed to receive light from the object under test for measurement of optical wavefronts received therefrom.
Another embodiment of the invention comprises a method of measuring waveshaping properties of a wavefront. In this method the wavefront is propagated through at least one two-dimensional modulation pattern thereby producing a self-image at a self-image plane of the two-dimensional modulation pattern. An image of the self-image plane is formed. Contributions from portions of the image of the self-image plane are reduced based on comparisons of a characteristic of the portions of the image with a threshold and a measure of the wavefront is determined based at least in part on the image of the self-image plane.
The details of the various preferred embodiments, both as to their structure and operation, can best be understood in reference to the accompanying drawings, in which like reference numerals refer to like parts, and in which:
The lensometer 10 further comprises beam tailoring optics, e.g., beam expanding and collimating optics 16 in the embodiment in
As shown in
Spectacles may range between about 45 and 65 mm in width and about 25 and 45 mm in height or up to 65 mm in diameter in some cases. In the case where the test lens 12 comprises spectacles, preferably the beam 18 produced by the beam expanding optics 16 that is passed through the test lens is between about 65 and 75 mm at the test lens. Accordingly, the beam expander and collimating optics 16 preferably also has a suitably large pupil. The aperture size or exit pupil of the beam expander and collimating 16 may, for example, have diameter between about 65 and 75 mm. In embodiments where the aperture or exit pupil are not circularly symmetric, the size may be characterized by a width of between about 45 and 65 mm and a height of between about 20 and 65 mm. Sizes outside these ranges, however, may be employed.
In the case where the test piece 12 comprises a lens blank, a larger beam may be preferred. In such cases, the aperture size or exit pupil of the beam expander and collimating optics 16 may for example have diameter between about 20 and 75 mm. In the case where the test piece 12 comprises a contact lens, a smaller beam may be preferred. In such cases, the aperture size or exit pupil of the beam expander and collimating optics 16 may for example have diameter between about 10 and 15 mm. Sizes outside these ranges, however, are also possible.
As illustrated in
In the lensometer 10 shown in
The beam reducing optics 26 preferably has a sufficiently large size to accommodate the beam 18 directed through the lens under test 12. In the case where the test lens 12 comprises spectacles, which may range between about 45 and 65 mm in width and about 25 and 45 mm in height or up to 65 mm in diameter in some cases, preferably the beam reducing optics 26 also has a suitably large pupil. The aperture size or entrance pupil of the beam reducing optics 26 may, for example, have diameter between about 60 and 80 mm. In embodiments where the aperture or entrance pupil are not circularly symmetric, the size may be characterized by a width of between about 70 and 90 mm and a height of between about 35 and 55 mm. Sizes outside these ranges may be employed in other embodiments.
In the case where the test piece 12 comprises a lens blank, the aperture size or entrance pupil of the beam reducing optics 26 may for example have diameter between about 70 and 100 mm. In the case where the test piece 12 comprises a contact lens, the aperture size or entrance pupil of the beam reducing optics 26 may for example have diameter between about 10 and 15 mm. Sizes outside these ranges are also possible.
In certain embodiments, the afocal beam reducing optics 26 shown in
The lensometer 10 further comprises at least one periodic diffractive element or two-dimensional modulation patterned element 28 disposed along the optical axis 22 and positioned to receive the light from the reducing optics 26. This periodic diffractive element or modulation pattern or element 28 may comprise, for example, a fine-pitch two-dimensional pattern with periodic features in the x and y directions such as a checkered board pattern or grid-like pattern. The diffractive element 28 may also comprise without limitation, a ruled two-dimensional diffraction grating, screen, grid, holographically generated transmission or reflective gratings, or the like. Alternative types of elements are also possible. Additionally, this periodic diffractive element 28 may have substantially same or different period in different, e.g., orthogonal x and y directions. One or more patterns may be employed. For example, two gratings with same or different periodicity in different directions may be superimposed to produce a pattern that is periodic in two directions. Other designs are possible as well.
The periodic diffractive element 28 is preferably disposed at or in proximity to a location in the optical system 10 where the test piece 12 is re-imaged. More particularly, this location preferably corresponds to a re-imaged pupil of the lens under test 12. The periodic diffractive element pattern 28 may, however, be disposed a distance from these locations although performance may be reduced.
As shown in
A light sensor 32 such as but not limited to a CCD, CMOS, or other detector array or camera may image any of the planes that correspond to the Talbot or “self-imaging” planes a distance n×d from the periodic diffractive element 28, where n is an integer. The self-imaging distance, “d,” is dependent on the spectral wavelength of the wavefront and the spatial frequency of the periodic diffractive element pattern. In some embodiments, a sensor plane of a sensor array is disposed at one of the self-imaging planes. Alternatively, the optical system 10 may comprise a camera having a lens that relays the self-image plane onto a detector located a distance away. Preferably, the sensor is located so as to image a region the self-imaging plane or within about 1% of the distance, d, from the self-image plane.
If the periodic diffractive element 28 is placed where an image of the lens under test 12 is formed, the lens under test together with the periodic diffractive element pattern are “self-imaged.” Likewise, the detector 32 will record the modulation pattern together with the test lens 12. If the lens under test 12 contains wavefront aberrations, the modulation pattern will be distorted relative to the periodic modulation element. The distortions on the periodic “carrier” intensity pattern can be extracted through computer algorithms applied to the recorded intensity values determined by the detector 32.
In various preferred embodiments, a signal from the detector 32 is sent to a data processor (i.e., computer) 34 for processing. The signal processor extracts from the signal, information about the phase of the wavefront after propagating through the lens under test 12 and the periodic diffractive element 28. Information regarding the wave-shaping properties of the test lens 12 is thereby obtained from the signal. To perform such processing, the processor 34 preferably accesses a software-implemented module 36 and outputs a signal representative of the phase of the wavefront to an output device 38. The output device 38 may comprise, but is not limited to a monitor, display, printer, computer, network, or other appropriate device.
By utilizing the various techniques described herein, a mathematical representation of the wavefront and of the aberrations of the wavefront having passed through the test piece 12 can be obtained. The wave-shaping properties, e.g., refractive properties and/or shape of the lens 12 may thereby be obtained. Similarly, the aberrations of the lens 12 including the higher order terms (e.g., 3rd order aberrations and higher) may be quantified.
Corrective lenses such as contacts and spectacles may therefore be characterized more precisely. The optical parameters of the lens 12 may be recorded or used to provide appropriate corrective optics for patients. The measurements of the lens under test 12 may assist in fabrication of the lens and may be integrated with the manufacturing process, e.g., for quality control. In certain embodiments, for example, the measurement may be employed to monitor the progress of the shaping of the lens and may be employed in a process of repeated measurement and refinement wherein the corrective lens is shaped based on measured waveshaping properties. This process may be iterative. In such embodiments, additional shaping, fabrication or other correction can be undertaken based on the measurements to obtain the desired lens parameters. The apparatus and techniques may similarly be applied to lens blanks during the fabrication stage and provide guidance regarding fabrication of the lens blank.
To provide improved results, a checkerboard pattern such as shown in
The periodicity of the pattern 28 may be on the order of about 20 to 120 microns although values outside these ranges are possible. Similarly, the checkered board pattern may comprise dark and light (e.g., transmissive and opaque or reflective and non-reflection regions) each between about 10 and 60 microns in size. The width of the patterned light blocking portions is preferably the same as the openings in the patterned element. The size, configuration and arrangement of the features in the pattern, however, may be different. The pattern 28 may, for example, include more or less features in different embodiments.
The checkerboard pattern approximates a two-dimension sinusoidal pattern 84 such as shown in
The sinusoidal intensity modulation element 28 produces a sinusoidal Talbot image. The carrier signal referred to above is thus sinusoidal in this case. Aberration in the wavefront manifests itself as modulation of this sinusoidal carrier. By using a sinusoidal carrier, the aberration information can be extracted more accurately, e.g., through Fourier transformation, with reduced or substantially no loss of information caused by high-order interference between the diffraction pattern of the periodic diffractive element 28 and the high-order aberrations of the wavefront. “Ringing” caused by sharp edges of non-sinusoidal intensity patterns that may result from non-smoothly varying periodic diffraction patterns can thereby be reduced or eliminated. Accordingly, the high-order information does not “diffract away” into high-order lobes. In principle, the sinusoidal optical element should enable measurement of extremely high-order aberration information.
Conventional technologies used to manufacture transmission gratings, however, may not be ideal for creating grayscale transmission functions. Binary patterns comprising a pair of discrete transmission levels may be more easily fabricated. In such binary patterns, the transmission of a given discrete spatial area is selected to be either a high value (“1”) corresponding to high transmission, e.g., about unity, or a low value (“0”) corresponding to low transmission, e.g. at or near zero. In various embodiments, a binary transmission function may comprise a plurality of discrete areas or “pixels” arranged in a desired pattern to resemble a continuous pattern. To arrive at an appropriate binary pattern that approximates, for example, a continuous two-dimensional sinusoidal function, a threshold transmission value may be selected. Values above the threshold are designated as high values (“1”) and rounded up to about unity transmission whereas transmission values below the threshold are designated as low values and rounded down, e.g., to about zero (“0”). Such threshold approximations applied to the continuous two-dimensional sinusoidal transmission function yield the rotated checkerboard pattern 86 comprising a lattice of diamond shapes as shown in
The checkered board pattern 86 advantageously closely resembles and approximates the continuous two-dimensional sinusoidal function. Computer modeling of the propagation of an aberration-free wavefront through continuous and binary periodic patterns confirms that residual phase error is reduced with these periodic diffractive element patterns. Examination of the Fourier transforms of both checkerboard and sinusoidal periodic elements exhibit reduced or minimize error in the vicinity of the fundamental frequency of the periodic pattern. Moreover, the residual phase error at the Talbot plane for the binary checkerboard diffractive element substantially matches that of the continuous two-dimensional sinusoidal diffractive element. The spatial frequency spectrum is thus preserved in the vicinity of the fundamental spatial frequency of the idealized sinusoidal periodic pattern. The spectrum in the vicinity of the fundamental frequency is not corrupted by harmonic components of the binary periodic element. A realizable and accurate approximation to a continuous sinusoidal element may therefore be fabricated using inexpensive manufacturing techniques.
In one embodiment, the checkerboard periodic diffractive element similar to that shown in
Another exemplary periodic diffractive element pattern 28 that may be employed is shown in
The periodicity of the pattern 28 may be on the order of about 20 to 120 microns although values outside these ranges are possible. Similarly, the pattern may comprise openings between about 10 and 60 microns in size separated by opaque lines between 10 and 60 microns wide. The width of the patterned light blocking portions is preferably the same as the openings in the patterned element.
Other types of gratings or periodic elements 28 may also be used. In other embodiments, for example, the element 28 need not be transmissive and may instead be reflective. The configuration of the lens measurement system 10 may likewise be different. In certain embodiments, a suitably constructed phase modulation element could be used to produce the desired intensity modulation. The phase modulation element may have variable path length that varies sinusoidally in two orthogonal directions. The periodic diffractive element 28 may also be formed differently and the pattern may be different as well. More than two may be used at various orientations with respect to each other. The pattern need not be linear. The periodic diffractive element 28 may, for example, comprise at least partially curved rulings. Similarly, the apertures in the periodic diffractive element 28 need not be square or diamond shaped but may comprise other shapes including but not limited to circles, ellipses, etc., as well as rectilinear shapes such as, e.g., triangles, hexagons, pentagons, etc. The pattern need not be completely periodic or regular. Other embodiments are possible. Other methods of manufacturing sinusoidal or non-sinusoidal patterns that may or may not approximate a continuous two-dimensional sinusoidal pattern may be used.
Other types of system configurations can be employed as well. In one exemplary embodiment shown in
In various embodiments, the lens holder 92 is configured such that the null lens 90 can be switched out and replaced with another null lens to alter the optical power of the null optics 88. For example, the lens holder 92 may comprise a wheel with a plurality of lenses mounted thereto and that is rotatable such that different of the lenses may be rotated into or out of the optical path of the beam 18. This wheel may be motorized or otherwise automatically driven or may be manually operated. One or more such wheels can be employed in series such that combinations of lenses may be inserted into the optical path of the beam to vary the optical power and aberrations. Also, although the null optics 88 is shown disposed in the optical path between the light source 14 and the test lens 12, the null optics may be positioned elsewhere, such as between the test lens and the first lens of the relay system 26. Also, other techniques can be used to alter the null optics 88. For example, the longitudinal position of one or more null lenses 90 along the optical path can be varied to alter the resultant optical power of the null optics 88. Other types of optical elements, beside null lenses may be employed as well. Preferably, however, the null optics 88 may be varied to vary the optical power so as to at least partially offset the optical power and/or aberration in the test lens 12.
As described above, other variations in the configuration of the lensometer 10 as well as the arrangement and type of optical components included therein may be used. In certain embodiments, for example, beam reduction optics 26 do not produce a collimated beam incident on the periodic diffractive element 28. Such a configuration is shown in
The lensometer 14 preferably produces very high spatial resolution, with certain embodiments having greater than about 300×300 measurement points for the portion of the test lens 12 being evaluated. The lensometer instrument 10 preferably offers enough resolution to measure relatively sharp phase errors and can accurately characterize higher order, high spatial frequency, aberrations and wavefront errors. A given wavefront may be described in terms of polynomials such as Zernike polynomials, each polynomial being of some order, n, with high order aberrations corresponding to polynomials of order three and higher. The wavefront may also be described in other manners know to those familiar in the art.
The Talbot or self-imaging based wavefront sensor described herein is superior to Shack-Hartmann interferometers, which use a lenslet array such as a 9×9 lenslet array. These Shack-Hartmann interferometers, which are conceptually based on geometric optics, have significantly reduced resolution and dynamic range that limit their ability to handle complex waveform shapes. For example, lenslet arrays used in conventional Shack-Hartmann interferometers have less than about 100 lenslets and correspondingly sample the wavefront at less than about 100 locations. In contrast, the periodic diffractive element 28 in the Talbot/self-imaging plane wavefront sensors described above may have about 10,000 apertures and thus sample the wavefront at about 10,000 locations, thereby increasing the resolution of the self-imaging system 10. Additionally, Shack-Hartmann interferometers exhibit limited linearity and have sub-aperture alignment issues. Scaling to large numbers of sub-apertures to measure high-order aberrations is also complex.
The lensometer 10 described herein offers other advantages as well. For example, measurements with the self-imaging based lensometer 10 are relatively fast. A sequence of short exposures can be quickly obtained with only one initial alignment. The captured images are preferably pre-screened for artifacts and processed. The results may be ready to display in less than one minute.
After the wavefront data is obtained and analyzed, the wavefront analysis results can be displayed on a screen or display for the user to view. The results can also be encoded into barcode format or transferred electronically such as through the internet. The Zernike data and other lens specifications may, for example, be encoded in a barcode on a label for the test piece. In some cases, this information may be sent to a lab for additional processing of the lens. In other exemplary embodiments, the lensometer 10 may be connected to an office practice management system via wireless network, intranet, internet, or ethernet. This office practice management system may include one or more computers or microprocessors. The office practice management system may also include storage or memory for recording measurements and patient data. The office practice management system may be linked with insurance providers, other healthcare providers, lens and eyewear manufacture or sales facilities, etc., and accordingly information may be conveniently communicated to such destinations.
In various embodiments, an instrument may be configured to operate as an ophthalmic instrument for measuring the refractive properties of the eye and also as a lensometer for measuring spectacle lenses and/or contact lenses. The instrument may operate in either of the two modes. Combining the lensometer function with the measurement of refractive properties of the eye offers powerful capabilities to the eyecare professional. A perspective view of a binocular instrument 300 that is both a lensometer and an ocular measurement system is shown in
To perform the ocular measurements, the patient looks into a pair of oculars or eye pieces 312 on a front face 314 of the instrument housing 310. The instrument 300 may include forehead rests 318 for comfortable positioning of the eyes with respect to the oculars 312. When performing precise wavefront measurements of the eye, the subject's eye is preferably focused and in a natural, comfortable state, thereby reducing or minimizing errors due to accommodation or eye movement. One method of ensuring that the subject is comfortable and relaxed is to present an image to the eye which allows the subject to fixate on a specific item. When viewing this image, the subject's vision is preferably corrected to a level allowing the person to fixate on the object. For example, the subject is preferably measured while viewing a natural scene at the desired distance for which the prescription will be generated. For an eye exam, the patient may view an eye chart or scene image placed at about 16 feet or greater from the subject. The ophthalmic diagnostic system 300 therefore preferably provides correction, such as spherical and astigmatic correction, through a lens to a real object at about 16 feet away. However, providing a 16 foot distance may pose a problem for some exam areas due to space constraints. This system 300 therefore preferably also provides a mode directing the subject's vision to an internal fixation target, if needed, for use in small rooms where, e.g., a 16 foot distance to a target, cannot be accommodated. An image formed at a distance of about 16 feet may be used as a target. Accordingly, various preferred embodiments include an internal/external fixation target design.
As shown in
The visual optics 212 further comprises a fixed lens 224, an inverting prism 226, and a movable lens 228 in this optical path 216. The inverting prism 226 comprises a plurality of reflective surfaces arranged to invert and flip an image (e.g., rotate the image about orthogonal x- and y- axes in a plane perpendicular to an optical axis 232 through the visual optics path 216). The optical elements are arranged along the optical path 216 such that visible light from the internal or external target passes through the movable lens 228, the inverting prism 226, and the initial lens 224 and is reflected off the beamsplitter 220 and into the eye 218.
The prism 226 is preferably rotatable about the optical axis 232 of the movable lens 228 to accommodate for differing pupilary distance. Both prisms 226, however, could alternatively translate horizontally (e.g., parallel to the x-axis) along with the movable lens to accommodate the subject's pupilary distance. The movable lens 228 is preferably held by a movable mount that can be translated axially along the optical axis 232.
Preferably, the movable lens 228 comprises a computer-controlled moveable lens. This moveable lens 228 may be motor driven in various embodiments. In operation, the lens 228 is preferably translated to an axial position at a location that is longitudinally displaced with respect to the prism 226 to provide spherical correction. The purpose of the prism 228 is to correct the image left to right and top to bottom, since the moveable lens 228 inverts and flips the image. The movable lens 228 may alternatively comprise a plurality of lens or other optical elements. In certain preferred embodiments, the movable lens 228 comprises two movable and rotating cylinder lenses to provide both spherical and astigmatic correction for the subject. The movable lens 228 may comprise a plurality of refractive optical elements or other optics that includes correction for other aberrations such as other high aberrations. In various embodiments, the movable lens 228 may include an adaptive optical element to provide optical correction as described above. This adaptive optical element may be used in conjunction with or instead of the moveable lens 228. This adaptive optical element may correct for higher order aberrations. For the majority of patients, however, spherical correction is sufficient to allow the patent to fixate on the target.
The adaptive optical element comprises an optical element with beam shaping properties that are re-configurable. The adaptive optical element may, for example, comprise a deformable mirror having a shape that may be selectively altered. In some embodiments, one or more transducers such as piezoelectric transducers may be disposed with respect to different portions of a mirror to apply stress to the mirror to alter the shape of the mirror. Other types of deformable mirrors are possible. Adaptive optic mirrors are available from Boston Micromachines Corporation, 108 Water Street, Watertown, Mass. 02472 as well as Flexible Optical B.V., P.O. Box 581, 2600 AN, Delft, The Netherlands. Other types of adaptive optical elements may be employed as well. The adaptive optical element, may for example, comprise refractive, diffractive, or reflective optical elements or combinations thereof. Various approaches to altering the optical parameters of the optical element are also possible. One or more adaptive optic elements may be employed as well.
In the optical path 216 to the right of the movable lens 228 in
Accordingly, depending on the setting, the visible look-through module in
A light source 240 may illuminate the internal fixation target 236. This illumination source 240 may, for example, comprise a light source such as a light emitting diode (LED) or an incandescent light bulb electrically powered and connected to control electronics for controlling the brightness of the source. Illumination intensity for the internal target images can be controlled, e.g. through a computer and calibrated to specific levels. Illumination may, for example, be controlled to simulate particular environments such as indoors, outdoors, offices, night driving, etc. When combined with the analysis of the pupil size determined from the wavefront sensor 210, detailed pupil reaction with respect to illumination level information can be recorded. For example, in various embodiments the sensor can image the pupil and thus pupil size can be correlated with illumination level.
As discussed above, the instrument 300 further comprises the wavefront sensor 210 such as the self-imaging systems described above. Accordingly, in various preferred embodiments, this wavefront sensor 210 preferably employs a two-dimensional periodic pattern 242 and a camera 244 at or focused on a self-image plane or Talbot plane of the periodic pattern. In certain preferred embodiments, this periodic pattern 242 comprises a checkered pattern as discussed above. This wavefront sensor 210 is disposed to receive light transmitted through the IR/Visible beamsplitter 220 and is preferably mounted onto either a manual or computer-controlled XYZ stage 246 to accommodate such positioning. As illustrated in
An adaptive optical element (not shown) may also be inserted in a portion of the path 256 through which light also passes to the wavefront sensor 210 such that the adaptive optical element operates as null optics for the wavefront sensor as described above. Software could “null” or cancel the wavefront for the sensor 210, which would result in the subject's vision being optimally corrected as well.
Control signals from a controller or control module (not shown) such as a microprocessor or control electronics may be used to control the operation of the adaptive optical elements. A feedback loop may be included from the detector 244 or associated computing components to the controller. Feedback may be provided from measurements obtained by the detector 244 or computing components that calculate values based on the shape of the wavefront projected through the eye 218. This feedback may be used to determine suitable adjustment to the wave-shaping properties of the adaptive optical element.
The adaptive optical element may correspond to null optics that provide correction to offset the aberrations in the eye 218. Correction of high-order aberrations and correction of lower order aberration terms such as focus and astigmatism may be provided by the adaptive optical element to neutralize substantially all the aberrations from the eye 218. In other embodiments, the adaptive optical element may be employed in conjunction with null optics, which correct for lower order aberrations like spherical aberration and astigmatism. Using the adaptive optics mirror in conjunction with one or more null lens that correct, e.g., for spherical aberration and astigmatism, would allow the use of less expensive adaptive optics elements such as shorter stroke adaptive optics mirrors.
In various preferred embodiments, the moveable wavefront sensor stage 246 shown in
The wavefront sensor 210 may further comprise illumination optics 266 that includes a light source 258 for illuminating the eye 218. This light source 258 may comprise, for example, a laser diode such as an infrared laser diode. Other types of lasers may be employed in this system 200 as well. In various embodiments, the laser produces a narrow substantially collimated beam 270. In some cases, therefore, collimating optics such as a collimating lens is not needed. The light source may alternatively comprise a super luminescent diode. Other types of light sources including other types of light emitting diodes may also be employed. Focusing or collimating optics 260 and a pin hole 262 may be included with the super luminescent diode or light emitting diode and disposed along an optical path 268 as shown
Preferably, the light beam 270 directed into the eye 218 is substantially narrow. In various preferred embodiments, the divergence of the beam 270 propagating to the eye 218 is sufficiently small and the beam is sufficiently narrow such that a cross-section across the beam orthogonal to its propagation direction is less than the size of the pupil. Preferably, the beam 270 has a cross-sectional dimension such as diameter or width that is substantially less than the average diameter of the pupil. The pupil may, for example, be on average between about 4 to 8 millimeters, e.g., 6 millimeters. In various preferred embodiments, the diameter or width of the beam 270 directed through the pupil is less than about 1 millimeter across and may be between about 200 to 600 micrometers (μm), e.g., about 400 μm in diameter. The beam 270 is preferably small so as to reduce the affect of aberration of the eye 218 on the beam. Preferably, the beam 270 is sufficiently small that the aberration in the eye 218 does not alter the beam entering the eye and does not increase the size or deform the shape of the light spot formed where the beam is incident on the retina. Preferably, this light spot formed on the retina is substantially small, for example, with respect to the ocular lens and cornea and approximates a point source. Blurring, increasing the size of the light spot, and/or distorting the shape of this spot may have a negative affect on the wavefront measurements.
A beamsplitter 264 may be inserted in an optical path 256 to the periodic pattern 242 and camera 244 so as to direct the beam 270 to the eye 218. Alternative configuration may also be employed.
To measure the refractive properties of the eye, the optical instrument 200 uses the several optical modules described above with respect to
This wavefront sensor 210 preferably provides very high-resolution wavefront information, as discussed above. This instrument 300 preferably offers enough resolution to measure relatively sharp phase errors near the edge of the pupil, for instance, and can handle high-frequency wavefront errors that might occur as a result of prior surgical procedures. After the wavefront data is taken and analyzed, the wavefront analysis results are then displayed on the screen near the device and can be encoded into barcode format or transferred electronically. The Zernike data may for example be encoded in a barcode along with the other information such as, e.g., patient ID, left/right eye, and may be sent to a lab for processing of the lens. In various embodiments, the instrument may be linked to an office practice management system via wireless network, intranet, or internet. Ethernet may be used. As described above, the office practice management system may include one or more computers or microprocessors and may also include storage or memory for recording measurement and patient data. The office practice management system may be in linked with insurance providers, other healthcare providers, lens and eyewear facilities manufacture or sales facilities, etc., and accordingly information may be conveniently communicated to such destinations.
Embodiments of the instrument 300 may include a small computer and/or electronics circuitry that handle the motion control of the motors or other translation devices, on/off and intensity control of the multiple illumination sources 240, 258, as well as reading sensors located throughout the system 300. In an embodiment shown in
Preferably, the ocular measurements may be performed without causing discomfort to the patient. Advantageously, since the measurement is fast, there is no need for rigid restraint on the patient during the exam. The comfort level of the patient is enhanced through the use of the invisible near-infrared laser 58, e.g., at a wavelength of about 850 nm, which forms a spot on the retina and illuminates the optical path 256 from the ocular surface to the detector in the wavefront sensor camera 244. Due to the efficiency of the optical measurement, a much lower power beam can be used to illuminate the retina. The power, for example, may be lower by a factor of approximately 4-7 compared to other conventional instruments that perform wavefront measurements on the eye. The combination of the use of infrared light and the lower illumination power level may lead to increased comfort and safety.
During an exam, a sequence of short exposures is preferably taken at one setting, which involves only one initial alignment of the patient. The patient is in the chair for only a few minutes, and the results are ready to display to the operator in less than one minute. Additional details regarding systems for measuring refractive properties of the eye is disclosed in U.S. patent application Ser. No. ______ entitled “Ophthalmic Diagnostic Instrument” (Attorney Docket No. OPH.024A) filed by ______ et al on even date herewith, which is incorporated herein by reference in its entirety.
Various techniques may be employed to improve the operation of the instrument 300. For example, in various preferred embodiments, this beam of light 270 is parallel to but laterally offset from the optical axis 222 of the wavefront sensor 210 as shown in
Other ways of more efficiently coupling light into the eye 218 are possible. For example, in some embodiments, the beam 270 from the light source 258 is introduced directly down the optical axis 222 of the sensor 210. In such cases, an optical element 280 (see e.g.,
As discussed above, in addition to measuring the refractive properties of the eye, the instrument 300 can be employed as a lensometer. In various embodiments, the instrument 300 is configured to position a spectacle lens or contact lens such that the waveshaping properties of such corrective lenses may be measured.
In embodiments such as those shown in
As shown in
The central upright support 326 is also connected to an earstem holder arm 340 having a crossbar 342 for supporting a pair of earstems 346 on the spectacles 322 (see
The adapter 320 further comprises a pair of retro-reflectors 348 disposed with respect to the left and right spectacle lenses 336, 338 such that the left and right spectacle lenses are between the retro-reflectors and the respective oculars 312. As a result, an optical path extends from the ocular 312, through the lens 336, 338 and to the retro-reflector 348 for each of the right and left spectacle lenses. The retro-reflectors 348 are supported by a holder 350 attached to the central upright support 326. The retro-reflector holder 350 may comprise a pair of arms extending from the central upright support 326 that position the retro-reflector 348 proximal to the spectacle lenses 336, 338.
A cross-section of one of the retro-reflectors 348 is shown in
The diffusely reflected light is collected by the curved front face 354 such that the beam 270 is expanded. The front face 354 may also have a shape and curvature and be positioned with respect to the rear face 356 such that light scattered from the diffusely reflective rear face 356 is collimated. In some embodiments, this curvature may be substantially spherical. In addition, the radius of curvature of the front face 354 may be preferably about the distance from the front face to the rear face 356 as measured along the central optical axis through the rod 352. The front face 354 preferably operates as a lens forming a beam from light reflected from the rear face 356. In various preferred embodiments the front surface 354 collimates the light reflected from the diffusely reflective rear surface 356. The front surface 354 may be shaped differently in different embodiments and may comprise other types of surfaces and optical elements. For example, the front surface 354 need not be a conventional refractive lens surface. The front surface 354 may comprise a diffractive surface having diffractive features formed thereon, thereby forming a diffractive or holographic optical element. The front surface 354 may also contribute to the beam shaping, however, work in conjunction with one or more other optical elements and/or surfaces. The front surface may also be planar in some embodiments. An additional lens element may provide beam shaping. Alternatively, gradient refractive indices of the rod 352 or other optical element may provide beam shaping. Other configurations are possible.
Preferably, however, a beam of light is propagated through the ocular 312. This beam of light 270 may originate from a light source similar to the light source 258 shown in
In other embodiments, the reflective element 348 is replaced with an external light source, such as a diode laser, and possibly a beam expander and/or collimator optics. Measurement of the corrective lens such as spectacle lens are performed using the beam provided by this additional light source. During measurement of a spectacle lens, the laser located within the wavefront sensor is turned off, blocked, diverted, etc.
In some embodiments, a corrective lens may be measured together with the eye by directing the beam through the corrective lens into the eye and measuring the return from the eye that again passes through the corrective lens. Such a configuration enables the practitioner to characterize the vision as corrected. Spectacles and especially contacts may be measured in this manner. The spectacles and contact lenses may be removed to measure the eyes without correction.
Disadvantageously, light from the beam passed through the lens or introduced into the eye may reflect or scatter back into the camera and can cause an unwanted glint artifact. This undesirable glint presents difficulty in the performing wavefront measurements. Special processing, however, may be employed to reduce the extent that glint, reflection, or back scattering from the spectacles, the eye, or from elsewhere in the optical path corrupts the measurements.
Reduced contrast may also result from light specularly or diffusely reflected or backscattered from surfaces of the spectacle lens, contact lens or lens blank as well as from scratches on the optical surfaces, or dust, particulates, or other scatter features in or on the lens or lens blank. Alternatively, light may also be reflected from or scattered by surfaces or features in or on the eye causing reduced contrast. For example, light may be specularly or diffusely reflected from surfaces on the cornea or ocular lens. Light may also be reflected or scattered by features in or on the cornea or the ocular lens as well as in the vitreous and aqueous humor or elsewhere in the eye. Such reflection and scattering may produce bright regions 380, such as shown in
A block diagram that describes the processing employed to characterize the wavefronts and determine the wave-shaping properties of the corrective lens or eye or other substantially transmissive optical structure is shown in
Logic may be executed in accordance with processes and methods described with reference to
Accordingly, the logic of the processor 34 can be appreciated in reference to
The principle of Talbot plane self-imaging is presented in references such as, e.g., Joseph W. Goodman, Introduction to Fourier Optics, The McGraw-Hill Companies, Inc., which include a treatment of interference and wave optics and which is hereby incorporated herein by reference. The formation of the self-image of the periodic element 28 involves the wave nature of light and the periodicity of the element. In a non-limiting, exemplary embodiment, the wavefront incident on the imaging detector 32 can be represented by the following diffraction equation:
In the case where the two-dimensional modulation pattern is a two-dimensional sinusoidal function, the intensity pattern at the first Talbot plane (e.g., where ZT=2 p2/λ) may be represented as follows:
In the case where an eye is the object under test, the pupil in the eye may be discernable in the recorded image. Similarly, the aperture of a lens such as a contact lens or a spectacle lens may also be apparent. For example, the image may comprise a dark region corresponding to the iris and possibly other portions of the eye that block light scattered from the retina. The image may further comprise a region corresponding to the pupil area where the light may exit the eye and pass through the two-dimensional modulation pattern onto to the detector. Similarly, when measuring a spectacle or contact lens, the dark region may correspond to regions outside the perimeter of the lens. Light transmitted through the lens will continue through the 2-D modulation pattern illuminating the pattern which may be discerned at the self-image plane. (The resultant image detected by the camera focused on the self-image plane may be similar to
In certain preferred embodiments, the location of the pupil or aperture is determined and a mask may be created with regions outside the pupil or aperture being nulled out (see second block 404). This mask, may comprise a digital filter comprising, for example, an array of values, e.g., 0's and 1's with 0's outside the perimeter of the pupil or aperture and 1's inside the pupil or aperture. At a later stage, this mask may be multiplied with the image data array in some embodiments to eliminate contribution from regions outside the pupil. Additional processing may be employed. For example, in some embodiments, the pupil or aperture is centered and possibly resized for display purposes.
As discussed above and illustrated in a third block 406, a Fast Fourier Transform or other transform may be applied to obtain a spatial frequency representation of the image. This step is also schematically illustrated in
In certain embodiments, however, prior to performing the Fourier transform or otherwise obtaining a spatial frequency representation of the image, regions to be masked out at a later stage are identified as represented by a block 405 in
After creating the glint or high-intensity mask and producing a frequency space representation of the image, intensity peaks in the spatial frequency mapping are isolated as discussed above and illustrated in
The peaks will generally be located on the fx and fy axes for two-dimensional gratings oriented along x and y directions. In the case where the periodic diffractive element is rotated, for example, by about 45° with respect to the x and y axis, the peaks will be off-center from the fx and fy axes. Exemplary peaks for a rotated 2D sinusoidal pattern rotated by 45° are represented by the following expressions:
The exponential terms
The wavefront information, e.g., the wavefront gradients
The arctangent function, however, ranges from −π to +π. Accordingly, the gradient information is limited to these values as illustrated by
The phase unwrap is susceptible to introducing error in the image in the case where pixels have low signal-to-noise values. In this region of signal-to-noise or low contrast, the edge of the diffractive element is blurred. This low contrast coincides with a low magnitude value (|M| in the complex exponential, |M|e−jθ) of the exponential terms
As illustrated by block 413 b in
As illustrated by circle 415 b and arrow extending from flow path 416 in
As indicated in
After this processing the wavefront may be reconstructed as illustrated by block 420, by determining the wavefront shape from gradient information and by combining the x and y components. The mask may be applied at this stage as well as indicated by an arrow extending from flow path 416 to block 420. The wavefront can be reconstructed using known algorithms for solving multi-dimensional partial differential equations including but not limited to “Successive Over-relaxation” and finite-element analysis.
A reference wavefront corresponding to the wavefront obtained by measuring a perfectly flat wavefront, perfect eye or optical element may be subtracted from the wavefront measured as illustrated by block 422 in
The last block 424 represents employing least square fitting for example to Zernike polynomials as described above to obtain a representation of the wavefront. The mask may also be applied at this stage in some embodiments as indicated by the arrow extending from flow path 416 to block 424. Accordingly, as illustrated by the block diagram in
In certain embodiment of the invention, real-time or near real-time analysis of images created with the wavefront sensor can identify problems in the images, provide closed loop feedback of positional information to the XYZ stage 246 to center the pupil in the image frame, set the focus, and analyze captured images or sets of images to determine outliers before averaging. A process flow diagram in
In one embodiment, during statistical monitoring the process segments a wavefront image using a histogram based approach to identify the pupil from the background of the image. The process stores values that represent attributes of the image, e.g., the diameter of the pupil, the location of the pupil within the image frame, and whether the image contains a saturated spot, a bright spot or glint (or other undesirable image characteristics which can be detrimental to the wavefront analysis). At state 1415, the process evaluates the outcome results of state 1410 to determine whether the image is a valid or invalid image. For example, the image can be an invalid image if it contains a saturated spot, a bright return or glint, or if the image is otherwise of poor quality. If the image is invalid, the process moves to a state 1420 and discards the image from the analysis. From state 1420, the process moves to state 1410 and proceeds as described above.
After the process evaluates whether an image is valid in state 1415, the process moves to a state 1430 and checks the location of the pupil and the focus of the image. In one embodiment, the process determines the pupil location by comparing a predetermined desired pupil location in an image (usually near or at the center of the image) to the actual pupil location (e.g., the XY coordinates of the pupil determined in state 1410) of the image being evaluated. If the values representing the actual location of the pupil in the image and the desired location of the pupil in the image deviate by a predetermined amount, the process moves to a state 1425 and commands the XYZ stage to move to a new X and/or Y position so that in subsequent images the pupil will be closer to the center or in the center of the image “frame.” The process creates the next image at the new location of the stage and processes the image as described herein. If the location of the pupil in the image deviates from the center of the image excessively so that the pupil is un-usable for determining a wavefront measurement (e.g., the pupil is not completely in the image), the stage is re-positioned in state 1425, the image is discarded and the process moves to state 1410 where it continues to monitor incoming images. If the location of the pupil in the image does not deviate by an amount such that the image is un-usable, the process can re-position the stage in state 1425 if necessary, the image is not discarded, and the process moves to state 1435.
In one embodiment, the process controls the focus of the image via an algorithm implemented in an image monitoring module in the data processor. The process controls focus by checking if a first image is in focus by determining the sharpness of the imaged pupil using various image processing techniques, e.g., analyzing high-frequency spatial components in the image. If the first image is out of focus, the process moves the Z axis of the XYZ stage a small amount in one direction to a new Z position. A second image is generated at the new Z position and the process analyzes this image to determine if the second image is more or less sharp. If the second image is sharper, the XYZ stage continues to move in the same direction as before and subsequent images are analyzed for sharpness until the sharpness of an image passes a predetermined sharpness threshold. If the second image became less sharp or un-focused after the stage movement, the process changes the direction of the XYZ stage and the stage moves in this new direction as subsequent images are generated. The stage continues to move until the subsequent images are in focus, e.g., pass a sharpness threshold. Alternatively, two images can be generated at two Z-axis locations of the wavefront sensor XYZ stage, and then those images can be compared to determine which one is sharper. Following this comparison, the process generates other images while moving the XYZ stage in the direction of the sharper image, until the process determines that the images pass the focus or sharpness threshold. If, after the initial stage movement, the image becomes more out of focus the stage changes direction and continues moving until the subsequent images are in focus. If the image is out of focus by a predetermined amount making the image unusable for calculating an accurate wavefront measurement, the image is discarded, and the process moves to state 1410, and proceeds as described above.
If the focus of a valid image is acceptable at state 1430, the process moves to state 1435 where one or more of the images of a pupil, e.g., a series of images, are stored in an image storage buffer, as in “image stack.” The image stack can be a sequential series of images, or can be a series of images of an eye that are not sequential because of, for example, intermittent invalid images. At state 1440, the process compensates for a patient's blinking by removing images that were generated during a certain time period after the patient blinked. This compensation can improve the quality of the images used for wavefront measurements. Detecting when a patient blinks and determining the appropriate image acquisition timing to compensate for the blinks can be accomplished based on the output of the above process. In state 1440 the process performs blink detection timing to capture images from the same point in time after a blink. When a patient blinks, the image is of poor quality because the pupil is either partially or completely obscured by the eyelid and the image is thus is deemed invalid by, for example, the above-described process. Wavefront images of the pupil taken too soon or too long after a blink can also be erroneous. A contributor to erroneous wavefront measurements is the eye's tear film, which typically degrades and dries out over time after a blink. If images are taken following a suitable delay period after a blink, the eye has a chance to stabilize. The delay period should not be so long that the tear film has begun to dry out or break down. During blink compensation, the process monitors the elapsed time between when the eye blinks and selects images generated after the eye has stabilized but before it dries out.
In one embodiment, a series of wavefront images is analyzed to identify an image that depicts a pupil at least partially obscured by an eyelid during a blink of the eye. This analysis may be part of the analysis conducted to determine valid images, or it may be conducted by another suitable image analysis process. The series of wavefront images is then further analyzed to identify another image that is generated after the eye has completed the blink such that this later generated image depicts a non-obscured pupil. In some embodiments, the identified image is the first image in the series of images that depicts a non-obscured pupil subsequent to the image depicting an at least partially obscured pupil. This image depicting a non-obscured pupil (e.g., a valid image), and/or valid images generated subsequent to this first image, can be stored and used for subsequent processing (e.g., determination of excessive movement between images, post-analysis qualification of images, averaging the images and determining a wavefront measurement).
In some embodiments, the process determines which images to store for further processing based on a predetermined time interval after blinking. For example, a timer can start after the process identifies a valid image depicting a non-obscured pupil in a series of wavefront images that were taken during the blink of an eye, and one or more of the images generated subsequent to the identified image are stored to a buffer at a specific interval after the blink occurs. For example, the time interval can be, e.g., less than .10 seconds, or equal to or between (in seconds) 0.10-0.20, 0.20-0.30, 0.30-0.40, 0.40-0.50, 0.50-0.60, 0.60-0.70, 0.70-0.80, 0.80-0.90, 0.90-1.00, 1.00-1.10, 1.10-1.20, 1.20-1.30, 1.30-1.40, 1.40-1.50, 1.50-1.60, 1.60-1.70, 1.70-1.80, 1.80-1.90, 1.90-2.00, 2.00-2.10, 2.10-2.20, 2.20-2.30, 2.30-2.40, 2.40-2.50, 2.50-2.60, 2.60-2.70, 2.70-2.80, 2.80-2.90, 2.90-3.00, 3.00-3.10, 3.10-3.20, 3.20-3.30, 3.30-3.40, 3.04-3.50, 3.50-3.60, 3.60-3.70, 3.70-3.80, 3.80-3.90, 3.90-4.00, or greater than 4.00 seconds. In one preferred embodiment, the time interval is about 1.00 seconds. With this process running, a patient can look into the wavefront measurement instrument and blink normally, eliminating the possibility of capturing images during, or directly after a blink which might contaminate the data. The images identified for analysis are therefore from about the same point in time after a blink. Images that do not meet the timing criteria can be discarded from the analysis. In an alternative embodiment, the process determines which images to store for further processing based on the number of images generated after determining that an image depicts a non-obscured pupil.
Moving to a state 1445, the process analyzes images to determine whether the movement of the pupil in successive images exceeds predetermined criteria. The pupil can move due to saccades or another eye movement. Excessive pupil movement can compromise the wavefront measurement. In one embodiment, the process determines the amount of movement of the pupil by analyzing the stored XY location of the pupil in each image of a stored stack of related images, and determines if the movement exceeds the criteria. If in state 1445 the process determines that there is excessive movement of the pupil, the process moves to a state 1450 wherein the image is discarded from the analysis and the next image in the stack of related images is analyzed. In state 1445, if the process determines that the movement of the pupil is not excessive, the image can be used for further processing, including determining a wavefront measurement of the aberrations of the eye, and the process moves to a state 1455.
At state 1455, the process stores the images that are to be used for further processing in a buffer as an image set or stack, and the images are further evaluated to determine if they should be combined to form an “average” image. The process will subsequently determine a wavefront measurement from the averaged image. Images are averaged to help remove image noise, for example, camera noise. At state 1455, the process performs further analysis of the images to determine if the images in the image set are “like” images, before they are averaged in state 1470. For example, the process can perform blob analysis to determine if the pupil is round or if there is a major inclusion in an imaged pupil, such as an eyelash or droopy eyelid. Opaque anomalies in an image such as cataracts, floaters, etc. can also be identified using image processing techniques, and these anomalies can be subsequently masked out so they do not affect forming the averaged image. Also, the identified anomalies can also be provided to the operator to alert the operator and patient to certain conditions that are present in the patient's eye. For example, the instrument can be used for early detection of cataracts, where a cataract appears as a dark spot in the image displayed to an operator, and/or the cataract is identified by image processing software as an anomaly that requires further investigation.
Following image qualification, the process moves to a state 1460 wherein the process determines whether the stored images in a set are acceptable for averaging. If they are acceptable, the process moves to state 1470 where the images are averaged and the process provides the resulting image to a wavefront measurement module for wavefront characterization such as described above. In one embodiment, the images are averaged by adding together the values of like pixels (e.g., pixels corresponding to the same eye position) of each image in the image set and dividing by the number of images. If the process determines in state 1460 that the set of images is not acceptable for averaging, the process moves to state 1465 where the image stack is discarded from further processing, and then the process returns to state 1440 to process another series of images.
In state 1475 the process sends the image resulting from the averaging process to the wavefront measurement module. At state 1480, the wavefront measurement module determines a wavefront measurement using processes such as described above. As discussed above, processing of Talbot images is also described, for example, in U.S. Pat. No. 6,781,681 issued to Horwitz, titled “System and Method for Wavefront Measurement.”
At state 1485, the process performs wavefront processing image sequence correlation. Here, the process compares the wavefronts from two or more average images (e.g., from two or more sets of images) to determine how similar the wavefronts are to each other and identify anomalies which were not identified in the previous processes. For example, problems relating to spurious accommodation, tear film and gaze angle can be determined by image sequence correlation. In one embodiment, wavefront processing image sequence correlation can be performed by analyzing each of the image stacks completely through the wavefront processing and comparing the wavefronts or Zernike polynomial representation. In an alternative embodiment, wavefront processing image sequence correlation can be performed on a partially processed sequence of images at any intermediate stage, such as in a Fourier space stage of processing the images. For example, wavefront data can be quickly processed to determine FFT's, and the FFT's can be compared to determine the similarity of the wavefronts. After correlating two or more wavefronts, at state 1490 the process provides the wavefront data for use to, for example, create a lens or for eye surgery to correct for the aberrations identified by the wavefront data.
Variations in the processing, however, are possible. The processing described above or portions thereof may be employed, may be excluded, or may be combined together with other techniques in different embodiments. The order of processing steps may vary as well.
Advantageously, various systems and methods described herein may be used to measure waveshaping properties including the aberrations of lens and/or of the eye Such measurement may be implemented using cost effective, highly accurate apparatus and methods. Various embodiments of the measurement instrument are designed specifically to meet requirements of eye-care and eyewear fabrication professionals, and at the same time to be affordable so that the instrument can be deployed in offices and facilities throughout the world. Embodiments of the invention can be implemented in relatively simple instrument designs that can reduce costs. As a result, ocular measurement using a wavefront sensor may therefore be a widely used technology for the benefit of eye care. The instrument may be used over the widest possible patient population, with special emphasis on diagnosing vision problems and abnormalities in children.
Higher order aberrations may also be measured with this wavefront sensor technology. Such higher-order aberrations can be generated by the lens manufacturing process. Knowledge of these higher-order aberrations therefore may be useful in implementing improved vision correction. Knowledge of higher order aberrations in the eye may also be useful in providing better correction.
Various techniques and designs disclosed herein may further increase the accuracy, precision, and dynamic range of the optical measurements. For example, illumination and filtering techniques may be employed to improve the results obtained.
The apparatus and methods described above, however, are only exemplary. Accordingly, the structures and processes employed should not be limited to those embodiments specifically recited herein. For example, the structures may include additional or different components and may not include all the features described herein. Processing may also be added or processing may be excluded or otherwise altered. The order of the process may be varied.
Moreover, those skilled in the art will appreciate that the methods and designs described above have additional applications and that the relevant applications are not limited to those specifically recited above. The present invention may be embodied in other specific forms without departing from the characteristics as described herein. The embodiments described above are to be considered in all respects as illustrative only and not restrictive in any manner.
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